This year marked the 70th anniversary of the Battle of Britain and the London Blitz. Several documentaries and shorts collections were released to capture the mood of the embattled nation and show how film-makers responded to the call for propaganda that would inform and inspire. However, the country's greatest director was accused of shirking his duty by remaining in Hollywood and contributing little to the war effort. But nothing could have been further from the truth.

Alfred Hitchcock declared war on Adolf Hitler five years before his compatriots. He would later claim that his work was apolitical, but just about every film he produced between 1934 and 1946 impinged upon the international situation. As successive governments strove to avoid offending the Führer by opposing his increasingly ambitious territorial demands, Hitchcock sought to warn audiences about the threat the Nazis posed to world peace. Similarly, after he was lured to Hollywood in the months before the outbreak of the Second World War, he attempted to win Isolationist America to the British cause.

Hitchcock wasn't just the Master of Suspense. He was also a master propagandist and his efforts drew envious praise from the Nazi propaganda minister, Joseph Goebbels. But, back in Britain, he was accused of betraying his country by refusing to renege on his contract with independent producer David O. Selznick. Some have even suggested that Britain's finest ever film-maker was denied his knighthood for so long because he was thought to have had such a poor war. Yet Hitchcock made the perilous journey across the Atlantic on several occasions and devoted himself to producing pictures for the war effort, including a number of shorts, for which he took little or no credit.

So the time has come to put the record straight and acclaim Alfred Hitchcock as Hitler's most implacable cinematic enemy.

Despite enduring Zeppelin raids and volunteering for the Royal Engineers, Hitchcock emerged from the Great War with a Boy's Own Paper view of conflict and an undiminished fascination with Germany. This intensified during his sojourn at UFA's famous Neubabelsberg Studios while assisting Graham Cutts on the 1925 melodrama, The Blackguard. Hitchcock spent hours in Berlin's galleries, museums, theatres and cabarets and quizzed his guests at all the best restaurants about German culture. He even picked up a rudimentary grasp of the language through reading the Brothers Grimm and ETA Hoffmann.

At the studios, he steeped himself in the Expressionist aesthetic while watching FW Murnau directing the landmark silent, The Last Laugh. He also made his own debut in Munich with The Pleasure Garden (1925) and fell in love with his assistant, Alma Reville. Thus, Germany helped define Hitchcock's cultural, epicine and sexual tastes and when asked at the height of his fame about his biggest cinematic influences, he simply replied: `The Germans. The Germans.'

In 1930, Hitchcock produced a Deutsch version of his early talkie, Murder!, and he regularly returned to Munich over the next few years. He must, therefore, have bitterly resented the Nazification of a city with so many happy associations and it's not too much of a stretch to see that his films of the Third Reich era were largely devised to expose the philistinism, criminality and savagery of the National Socialists. The Nazis had crushed the Weimar spirit that had enabled Hitchcock to discover himself as both an artist and a man and he would never forgive them.

Hitchcock joined Gaumont as Hitler became German chancellor in January 1933 and he responded by harking back to more innocent times with the Jessie Matthews musical Waltzes from Vienna, which showed a more benevolent side of the Teutonic character. However, two of Hitchcock's closest friends, Ivor Montagu and Sidney Bernstein, were prominent members of the British Committee for Victims of German Fascism and they regularly attended the brainstorming sessions he hosted in his Cromwell Road flat while developing screenplays. As he mythologised his career, Hitchcock would claim that his work was devoid of political content. But his British espionage pictures blatantly played on the insecurities of viewers who had just watched newsreels about Germany's rearmament programme, its withdrawal from the League of Nations and its increasingly aggressive search for Lebensraum.

The British Board of Film Censors forbade the overt criticism of a foreign regime and continued to do so until hostilities commenced. However, Hitchcock left audiences in little doubt about the identity of the enemy in The Man Who Knew Too Much (1934), The 39 Steps (1935), Secret Agent, Sabotage (both 1936) and The Lady Vanishes (1938). Yet when war was declared on 3 September 1939, Hitchcock was in Hollywood making Rebecca and rather than having the satisfaction of pointing to his recent output and saying `I told you so', he found himself being pilloried for his failure to rally to the colours by some of the same people who had prevented him from being more outspoken in his denunciation of the Reich.

Perhaps things might have been different had Hitchcock followed Selznick's advice and made a film about the Titanic, as the scenes of casualties stranded in the frozen waters would have registered with British audiences becoming accustomed to newsreels of shipping being sunk by u-boats. But by opting for Dauphne Du Maurier's penny dreadful about a toff getting away with murder, Hitchcock laid himself open to accusations of self-indulgence as his fellow countrymen prepared to face the Nazi onslaught. Few were willing to see the storyline as an allegory of Chamberlain's attempts to appease Hitler or that Manderlay stood as a symbol for a Europe in flames and not even the fact that Rebecca won the Oscar for Best Picture could persuade the detractors that it had helped keep plucky Britain in America's thoughts.

Hitchcock was stung by the hypocrisy of much of the reprobation. Well past the age to join the forces, his presence in London would have been all-but pointless during the Phoney War, as cinemas and theatres had been closed down and production had ground to a halt. What's more, Selznick essentially controlled his movements. So, when Michael Powell arrived in Hollywood to complete The Thief of Bagdad (1940), Hitchcock not unreasonably concluded that he also stood a better chance of finishing a flagwaving feature in California than he would back in Blighty.

Consequently, he talked Selznick into allowing him to make Foreign Correspondent (1940) for Walter Wanger and began seeking ways of boosting the British cause without falling foul of either the Hays Code or the Neutrality Act. Ultimately, he had to settle for the enemy being Borovian not German, but no one missed the point of his tale about an American reporter who is sent to Europe and winds up thwarting a bogus peace movement's bid to abduct the Dutch statesman who holds the balance of power.

The action was inspired by Vincent Sheean's memoir, Personal History, but allusions were added throughout shooting to the calamitous events of spring 1940. Biographer Donald Spoto rightly says that `the finished film (except for the last minute) has as much to do with the politics of the war as Tosca has to do with Napoleon's campaign in Italy'. But critic Raymond Durgnat is equally correct in his assertion that `propaganda which sets out to motivate the complacent and apathetic, and sharpen the urgency of the already concerned, must inspire a blend of healthy fear and resolve, an immediate panic combined with a long-term confidence'. And this is exactly what Foreign Correspondent succeeded in doing, especially after Hitchcock and rabidly Germanophobic scriptwriter Ben Hecht added a coda that revealed the director's fraught emotions after his first visit to wartime Britain.

Hitchcock knew all about the perils of crossing the Atlantic, as the ship carrying the cameraman dispatched to record background footage for Foreign Correspondent had been torpedoed and he had lost all his equipment. Yet he embarked for London in June 1940 and promptly arranged for his mother to move from the capital to the comparative safety of Shamley Green, near Guildford. He also tried, less successfully, to persuade Robert Donat to come to Hollywood to make Greenmantle as a rousing sequel to The 39 Steps. But much of his time was spent being inconvenienced by rationing and blackouts and he returned to the United States on 3 July feeling so despondent that he insisted on the addition of a new speech for hero Joel McCrea.

Eerily anticipating Edward R. Murrow's legendary radio broadcasts, it described how a place as nice as Vermont, Ohio, Virginia, California and Illinois was being ripped up `like a steer in a slaughterhouse'. But personalising Britain's torment for the average American wasn't enough for Hitchcock. He wanted them to step up to the plate and prove that they really did live in the Land of the Free and the Home of the Brave. So, McCrea's exhortation concluded that while death was coming to London, America had to keep its lights burning, as they were `the only lights left in the world!'

The scene was filmed on 5 July and the Blitz began five days later. Yet Hitchcock's impassioned plea only brought more accusations that he was a coward. The veteran actor Seymour Hicks informed the press that he had heard rumours that Hitchcock had recruited Charles Laughton and Herbert Marshall to make Gone With the Wind Up, while the author JB Priestley suggested that stayaways like Hitchcock and Gracie Fields would rather face the footlights than the searchlights. When Foreign Correspondent premiered in London, industry luminaries like Paul Rotha and Dilys Powell wrote to the Documentary News Letter castigating McCrea's salvo as the rantings of `an irresponsible American news-hound' and fumed that Britain's civilian army could defend itself against Nazism without American assistance.

But the signatory whose remarks hurt Hitchcock most was his onetime boss, Michael Balcon. On 25 August, Balcon launched a vicious attack on the deserters who had chosen `to remain in Hollywood instead of returning home to aid their country's war effort'. He singled out Hitchcock alone for special opprobrium: `I had a plump young technician in my studios whom I promoted from department to department. Today he is one of our most famous directors and he is in Hollywood while we who are left behind short-handed are trying to harness the films to our great national effort.'

It was a spiteful tirade and it did much to tarnish Hitchcock's reputation. Moreover, it was appallingly ill-informed for one who considered himself to be an establishment insider, as Lord Lothian, the British Ambassador to the United States, had already announced that `all Englishmen over the age of 31 should remain at work until new regulations about military age were issued', while the the British consul in Los Angeles had informed expats that it would be foolish for them to `all rush back to England, which had plenty of manpower for the foreseeable future but no equipment'. Balcon should also have known that Prime Minister Winston Churchill had sanctioned a continued British presence in Hollywood, as he believed that well-made films would leave a much deeper impression on audiences than well-meaning ones.

Balcon later apologised half-heartedly, but Alma Reville never forgave him and applied immediately for US citizenship. Hitchcock himself responded by saying that Balcon was merely envious and branded him `a permanent Donald Duck', because his efforts to crack Hollywood had failed so often and so badly. Moreover, he pointed out that `the British government has only to call upon me for my services. The manner in which I am helping my country is not Mr Balcon's business and has nothing to do with patriotic ideals.'

In fact, Hitchcock had been busy behind the scenes. He co-ordinated a fundraising drive with Dame May Whitty to bring children from the Actors' Orphanage to safe homes in North America and, during his visit to London, he cut through the red tape to speed the passage of 60 children to Ottawa. He also attended the party Selznick threw for the first anniversary of the release of Gone With the Wind, which benefitted the British War Relief Fund, and he regularly attended secret meetings of Hollywood's English Colony to discuss ways in which they could slip mentions of the war into their films without offending the censors, the Isolationists or the Communists.

This cabal included directors Victor Saville and Robert Stevenson and actors Reginald Gardiner and Boris Karloff (whose brother worked for MI6), and together they conceived Forever and a Day (1943), a portmanteau costume drama designed to promote Anglo awareness among American audiences. Unfortunately, problems with Cary Grant's schedule forced Hitchcock to pass his segment to René Clair, but he remained on the board of governors of Charitable Productions, which oversaw the picture and ensured that its proceeds went to the right causes.

Even more significantly, Hitchcock renewed acquaintance with Sidney Bernstein, who was now acting as film advisor to the Ministry of Information. While he was waiting for the sets to be built for Mr & Mrs Smith (1941), Hitchcock agreed to tailor David MacDonald's short, Men of the Lightship, for the American market, after it had been rejected by both RKO and 20th Century-Fox. Roping in Rebecca scenarist Robert Sherwood and actor Robert Montgomery, Hitchcock spent $4,428 of his own money revising this tribute to the heroic crew of the East Dudgeon lightship. However, he refused reimbursement or credit and similarly insisted on remaining anonymous on the US version of Harry Watt's Target for Tonight, the story of a raid on an oil storage facility on the Rhine, which was seen by 50 million viewers across the Americas. Demonstrating that Britain was fighting back, it received an Honorary Academy Award `for its vivid and dramatic presentation of the heroism of the RAF'.

Given the secrecy surrounding much of his war work, it appeared as though Hitchcock spent 1941 licking the wounds inflicted by his decriers, as both the screwball comedy Mr & Mrs Smith and the psychological thriller Suspicion skirted the conflict (although a rejected ending for the latter had Cary Grant's sinister husband atone for his sins by becoming an air ace in the Battle of Britain). However, the situation changed dramatically during the pre-production of Saboteur (1942), as America entered the war following the Japanese attack on Pearl Harbor and the majority of the restrictions that had so frustrated Hitchcock's anti-Nazi crusade were finally removed.

Resisting Selznick's suggestion that he should either remake The Man Who Knew Too Much or adapt Hitler's pernicious manifesto, Mein Kampf, Hitchcock opted for a Stateside variation on The 39 Steps, in which Robert Cummings traverses the country to prove that Norman Lloyd is guilty of the factory explosion for which he is being blamed. He did allude to the Führer, however, as Fifth Columnist Otto Kruger's quip about the `moron millions' echoed Hitler's contention that America was nothing but `millionaires, beauty queens, stupid records and Hollywood'. But Hitchcock also managed to offend the US Navy by implying that saboteurs had been responsible for the fire aboard the SS Normandie in New York harbour and the shots of Lloyd sneering at the capsized liner through a taxi window were summarily removed. The film's release coincided with the thwarting of a Abwehr sabotage plot codenamed Operation Pastorious, but this proved the least subtle of Hitch's wartime offerings. As critic Dilys Powell put it: `This is Hitchcock at his most Hitchcock, which doesn't necessarily mean at his best.' He responded, however, with his most devastating dissection of the Nazi psyche, although such was the finesse of Shadow of a Doubt (1943) that its propaganda value has often been overlooked.

The story of a beloved uncle who is really a serial killer was developed by Thornton Wilder and Sally Benson, who had respectively been responsible for those classic exercises in quaint Americana, Our Town and Meet Me in St Louis. But it was Hitchcock who envisaged Joseph Cotten as an enemy within, whose simmering hatreds mirrored those of a fascistic fanatic. His chilling speech about decadent wives, for example, could just as easily have been about the Jews. No wonder Hitchcock subtitled the film `The Man Behind Your Back' and he used another of Cotten's diatribes to niece Teresa Wright to alert a sleepwalking America to the dangers of insularity and lethargy.

Yet audiences and critics were so seduced by Hitchcock's acute snapshot of small-town life that they failed to notice his murkier intent. Thus, he decided to make the message more obvious in Lifeboat (1943), only to find himself once again being subjected to a backlash from armchair patriots who knew little or nothing about the dark art of propaganda.

The story of a u-boat commander's encounter with the survivors of the ship he has just torpedoed, Lifeboat was intended as a microcosm of the war and a summation of Hitchcock's changing attitude to the Germans he had feared as a boy, admired as a young man and now thoroughly detested. As he later told François Truffaut: `We wanted to show that at the moment there were two world forces confronting each other, the democracies and the Nazis, and while the democracies were completely disorganised, all of the Germans were clearly headed in the same direction. So here was a statement telling the democracies to put their differences aside temporarily and to gather their forces to concentrate on the common enemy, whose strength was precisely derived from a spirit of unity and of determination.'

However, few viewed the matter as straightforwardly as Hitchcock. The Office of War Information complained that `the group of Americans in the lifeboat paint a picture which the Nazi propagandists themselves would like to promote', while Bosley Crowther seethed in the New York Times that Hitchcock had `sold out democratic ideals and elevated the Nazi superman'. Amidst the benighted hubbub, only the great News Chronicle critic, Richard Winnington, recognised that Hitchcock had delivered some `good and timely propaganda'.

Despite being as divisive as Foreign Correspondent, Lifeboat similarly earned Hitchcock an Oscar nomination. But his contributions to the war effort continued to be either ignored or impugned. In December 1943, he flew back to Britain to honour his promise to Sidney Bernstein to direct for the Ministry of Information. Realising that Hitch had little Home Front experience, Bernstein sensibly teamed him with old friend Angus MacPhail (who had coined the term `MacGuffin') on a tribute to the French Resistance.

The flashbacking tale of a British airman who is duped into trusting a Nazi agent, Bon Voyage may have anticipated Rashomon (1950) in disproving the old maxim that the camera never lies, but it was more a philosophical treatise on the nature of truth than a piece of hard-hitting propaganda and it was only screened fitfully in France after D-Day. Yet it fared better than Aventure Malgache, which again starred the Molière Players in a study of internecine treachery on the island of Madagascar. Hitchcock had hit upon the idea after witnessing the fractious relations between the different Gallic groups based in London. But his jaunty take on the Vichy collaborators and their Free French and Maquis adversaries appalled General De Gaulle's staff and it was shelved until 1993.

Keen to be treated as one of the boys, Hitchcock earned only £10 a week during his three-month stay. But he returned to Hollywood in low spirits, perhaps chastened by the unassuming courage of the spinster cousins who had casually remarked while dining in the grandeur of Claridge's that the noise made by the planes and ak-ak guns booming overhead sounded very different here than it did at home.

Hitchcock's disquiet was presumably exacerbated by the fact that his next feature, Spellbound, contained his most veiled references to the enemy within since Jamaica Inn (1938). Consequently, he agreed to shoot the War Bond promo, The Fighting Generation (1945). Filmed by Gregg Toland and running just 52 seconds, it featured Selznick's new lover, Jennifer Jones, as a nurse tending a soldier wounded on Saipan. In the course of her monologue, she urged viewers to bring the boys home `by buying a share of their faith in victory'.

Hitchcock refused credit or remuneration for his services and he similarly worked gratis after he was personally selected by Secretary of State, Edward Stettinius, Jr., to make Watchtower Over Tomorrow (1945), an OWI short on the need for a postwar organisation to guarantee global peace. Working through the night on Boxing Day 1944, Hitchcock and Ben Hecht devised a scenario set in 1960, in which a united nations body prevents a third world war. However, the State Department was keener to suggest that the Dumbarton Oaks plan would prevent future crises and seemingly few of their ideas made it into the finished film.

One good thing did come from the trip to the capital, however, as the furtive atmosphere and sense that something big was about to happen gave Hitchcock the idea for the MacGuffin in Notorious (1946).

Although the war in Europe appeared to have turned decisively in the Allies' favour, Hitchcock aimed to use John Tainter Foote's story, `The Song of the Dragon', to caution against laxity by suggesting that the Nazis were sufficiently cunning to regroup in Latin America and connive at world domination some time in the near future. However, plans to secrete a renegade army in the Amazonian rainforest were abandoned once Hitchcock learned about uranium.

Intrigued by rumours of German experiments with heavy water in Norway and secret tests being conducted in the New Mexico desert, Hitch and Hecht went to the California Institute of Technology to ask Nobel Prize-winning physicist Robert Millikan about the possibility of splitting the hydrogen atom. According to Hitchcock, the professor was so aghast that Hollywood had rumbled the Manhattan Project that he called the FBI and had the pair placed under round-the-clock surveillance for the next three months. However, a man with Hitchcock's paralysing fear of authority would hardly have risked placing himself in such a predicament and the story is clearly apocryphal.

Selznick thought the entire concept for was ludicrous, but he submitted a draft screenplay to J. Edgar Hoover, who gave his assent because the scenario showed Germans trying and failing to produce a bomb rather than Americans succeeding. A dismayed Selznick sold the project to RKO. But Hitchcock's hopes of astonishing the world with his sensational discovery were dashed by Cary Grant's schedule preventing him from starting work before October 1945 - by which time both Hiroshima and Nagasaki had been decimated and the war was over. Uranium in wine bottles still made for a fiendish plot device, but all that Notorious really demonstrated was that American spies could be just as ruthless in the execution of their duty as anyone else's.

The carnage caused by the atomic bombs paled, however, beside the crimes against humanity committed by the Nazis in the concentration and extermination camps. The Allies had known about their existence, but it was only when they were liberated that the full extent of their horrors was revealed. Sidney Bernstein visited Bergen-Belsen in April 1945 and accepted a commission from the Psychological Warfare Division of the Supreme Headquarters Allied Expeditionary Forces to produce a feature documentary using British, American and Russian footage from Dachau, Ravensbrück, Buchenwald, Ebensee, Mauthausen and Auschwitz. He asked Hitchcock to co-ordinate his seven-reel `German Atrocity Film', but Stewart McAllister and Peter Tanner had already begun to assemble the material by the time he arrived in June to act as `treatment advisor'.

Fully aware of the manipulative power of montage, Hitchcock's urged the editors to use as many long takes as possible to avoid accusations of fakery. Similarly, he suggested the inclusion of images showing residents from the nearby communities surveying the scenes to implicate ordinary Germans in the hideous acts that had been perpetrated in their name. He also worked with Colin Wills and Richard Crossman on the commentary. But the project was abandoned in September 1945 after the Americans decided to concentrate on Billy Wilder's Die Todesmühlen (1946) and the British government withdrew Bernstein's funding and facilities. The silent print was stored at the Imperial War Museum with the label F3080 until 1984, when Memory of the Camps finally premiered at the Berlin Film Festival.

Hitchcock died four years before this excruciating testament was shown. Yet his name was used as a key selling point, as it was when a version with narration by Trevor Howard aired on PBS in May 1985. Such was Hitch's self-effacement throughout the Second World War that it's highly likely that details of further secret assignments lie hidden in the archives. But it should already be clear that while he may never have seen frontline action and only rarely shared the nightly terrors of bombing raids with his fellow Londoners, Alfred Hitchcock always answered the call when it came and was never found wanting. It's just a shame that nobody thought to gather his unreleased wartime contributions on DVD. Maybe they will in time for a future anniversary.