Forty years ago, London Weekend Television launched the finest period drama ever produced by ITV. It was originally conceived as a sitcom entitled Behind the Green Baize Door. But co-creators Jean Marsh and Eileen Atkins were persuaded that events at 165 Eaton Place should be not only be taken more seriously, but should also include the residents both above and below stairs to present a popular history of Edwardian society. The format was revised by writer Alfred Shaughnessy and Upstairs, Downstairs went on to win numerous BAFTAs, Emmys, Golden Globes and a host of other prestigious awards.

Moreover, the 68 episodes screened over five seasons to 1975 became such a part of the British viewing public's collective consciousness that when ITV returned to the topics of class and domestic service with Downton Abbey nearly every review judged the programme against Upstairs, Downstairs. Ironically, of course, when the BBC revived Marsh and Atkins's show over Christmas last year (with Atkins finally able to participate, as a prior commitment to play Queen Victoria had meant she had been forced to pass the role of Sarah on to Pauline Collins) it was immediately compared to Downton.

There's no question which is the superior programme and it's wonderful to report that the DVD release of the BBC incarnation coincides with the reissue of the original series in a value-for-money sans extras edition - although Network is keen to point out that a 21-disc set is also available including five exclusive documentaries, as well as selected commentaries and archive interviews.

The first season opened with `On Trial', in which Sarah Moffat (Pauline Collins) arrives at the Belgravia home of Liberal MP Richard Bellamy (David Langton) and his wife, Lady Marjorie (Rachel Gurney). Despite trying to pass herself off as French, she is exposed as a Cockney sparrow and is quickly taught her place by butler Angus Hudson (Gordon Jackson), who runs the servants' hall he shares with cook Kate Bridges (Angela Baddely), lady's maid Maud Roberts (Patsy Smart), house parlour maid Rose Buck (Jean Marsh), Pearce the coachman (Brian Osborne), Alfred the footman (George Innes) and Emily the Irish kitchen maid (Evin Crowley). However, the Bellamy children - James (Simon Williams) and Elizabeth (Nicola Pagett) - prove just as capable of landing themselves in hot water as the capricious Sarah, with Elizabeth refusing to conform to convention in `The Path of Duty' and then dallying with the Suffragettes before falling for poet Lawrence Kirbridge (Ian Ogilvy) in `The Key of the Door', while James embarks upon an affair with Sarah (who has now become a music-hall star) in `For Love of Love'.

However, even the older Bellamys have their weaker moments, with Richard nearly becoming involved in a scandal after taking pity on crying under-house maid Mary (Susan Penhaligon) in `A Cry for Help' and Lady Marjorie being seduced by James's dashing army friend, Captain Charles Hammond (David Kerwin), in `Magic Casements'. Yet the standout episodes of the first series are undoubtedly `A Suitable Marriage', in which Alfred has a homosexual liaison with snooping German baron Klaus von Rimmer (Horst Janson); `I Dies From Love', in which Emily hangs herself after she's forbidden from romancing a visiting couple's footman; and `Why Is Her Door Locked?', in which Mrs Bridges steals a baby while tormented with guilt over Emily's suicide.

Much of the second series was taken up with Elizabeth's unhappy marriage and the ongoing adventures of the irrepressible Sarah. It's now 1908 and Edward Barnes (Christopher Beeny), Ruby Finch (Jenny Tomasin) and Thomas Watkins the chauffeur (John Alderton) have settled in downstairs, while Elizabeth has had a daughter named Lucy. However, Sarah has also fallen pregnant following her fling with James and she is only brought back to London from the country to care for the baby after Nanny Webster (Daphne Heard) proves unable to cope in `Out of the Everywhere'.

In fact, the storytelling became increasingly episodic in the second season, with King Edward VII (Lockwood West) coming to dinner in `Guest of Honour', Watkins recovering billets doux from Captain Hammond's blackmailing ex-footman Desmond Perry (Michael Dooley) in `The Property of a Lady' and Hudson adopting airs and graces to impress his brother Donald (Andrew Downie) in `Your Obedient Servant'. However, the narrative thread was restored in `The Fruits of Love', as Lady Marjorie is forced to sell Eaton Place to help her bankrupted father and Armenian arriviste Julius Karekin (Donald Burton) returns them to Elizabeth in the hope of contracting an advantageous match. But, as the household mourns the passing of the monarch in `A Family Gathering', Elizabeth announces her imminent departure for America just as James returns from his face-saving exile in India with unsuitable fiancée Phyllis Kingman (Delia Lindsay) in tow.

Greater upheaval shakes the family at the start of the third series, however, as Lady Marjorie perishes in the sinking of the Titanic in `A House Divided'. But James is soon seeking solace in Hazel Forrest (Meg Wynn Owen), the secretary his father has hired to help with his biography of his late father-in-law, Lord Southwold. She initially rebuffs his proposal in `A Family Secret'. But James persists and they marry, only for their relationship swiftly to decline after Hazel participates in a foolish prank during a country house weekend in `The Bolter' and she loses their child in `Distant Thunder'.

With James becoming increasingly smitten by Richard's ward, Lady Georgina Worsley (Lesley Anne Down), a romance also develops below stairs between Edward and the new under-house parlour maid Daisy Peel (Jacqueline Tong). However, he is lucky to keep his job after an encounter with dastardly colonel Harry Tewkesbury (Bernard Archard) in `What the Footman Saw', while Rose also considers her future after meeting dashing Australian sheep farmer Gregory Wilmot (Keith Barron) in `A Perfect Stranger'.

However, the war clouds that have been gathering over Europe finally break at the end of the series and James and Edward have enlisted by the time the fourth season begins. James discovers the cost of careless talk in `News From the Front' and the fiercely patriotic Hudson learns a similar lesson after his scare stories about German atrocities upset a local trader and his junior charges in `The Beastly Hun'.

With Ruby away working in a munitions factory, Georgina and Rose also decide to do their bit and train as a VAD nurse and an omnibus conductorette respectively in `Women Shall Not Weep' and `Home Fires'. But tragedy is never far away, with Rose's grief over Gregory's demise in `The Glorious Dead' coinciding with Edward return from the Western Front with severe shell shock in `Another Year', Hazel's involvement with timid Flying Corps officer Jack Dyson (Andrew Ray) in `If You Were the Only Girl in the World' and James's disappearance at Passchendaele in `Missing Believed Killed'.

By the close of the series, in `Peace Out of Pain', Richard has married war widow Virginia Hamilton (Hannah Gordon) and James has been left bereft by Hazel's death in the 1919 flu epidemic. But the next 11 years bring further unhappiness to the family, with James failing dismally in a bid to follow his father into politics in `A Place in the World' and then inviting a scandal by cavorting with best friend Bunny Newbury (John Quayle)'s wife Diana (Celia Bannerman) in `An Old Flame'. Hudson's intentions are also misunderstood when he's seen at the British Empire Exhbibition at Wembley with housemaid Lily (Karen Dotrice) in `Disillusion' and his diminished status makes it difficult to control his underlings during the 1926 General Strike in `The Nine Days Wonder'.

Frederick Norton (Gareth Hunt) is now assisting Hudson and Edward. But Richard and Virginia have less need of such a large staff after the Liberals are forced into opposition and, with James in America and Georgina increasingly in the company of the Marquis of Stockbridge (Anthony Andrews) after she is involved in a motoring accident (in `Joke Over'), it becomes clear that the family has to move with the changing times. The writing is on the wall after James loses Rose's savings in the stock market crash in `All the King's Horses' and, when Georgina rejects his entreaties in `Whither Shall I Wander?', the story comes to a tragic close.

With budgetary constraints meaning that episodes were largely filmed as live theatre, it's easy to snipe at the occasional fluffed line and glance into the camera. But the acting through all five years was of the highest order, with David Langton bringing stiff decency to the role of the bright politician who had married well, Simon Williams making James an affable cad and Lesley Anne Down creating a bright young thing whose follies always seemed to damage other people more than herself.

As for the staff, Gordon Jackson is magnificent as Hudson, combining tactful deference with a Scottish sternness that could occasionally crack to reveal a gentle man who came as much to outlive his time as his employees. The dependable Angela Baddeley and Jean Marsh brought working-class common sense to proceedings as Mrs Bridges and Rose and their byplay with Edward, Daisy and Ruby brought some much-needed levity and a sense of the growing confidence of the proletariat in the inter-war period.

The scripts, by the likes of Alfred Shaughnessy, John Hawkesworth, Fay Weldon, Terence Brady, Charlotte Bingham, Rosemary Anne Sisson and Elizabeth Jane Howard, were always literate and densely plotted, while the direction of Bill Bain, Christopher Hodson, Raymond Menmuir and Derek Bennett was always stately and focused on performance rather than grandiloquence. John Clements's production design was also impeccable, with the drawing room and kitchen at Eaton Place being both authentic and welcoming. Even Alexander Faris's Ivor Novello-winning score fitted the bill perfectly and it was disappointing to note that the new BBC series had dispensed with `What Are We Going to Do With Uncle Arthur?' from the closing credits.

If Upstairs, Downstairs was essential family viewing, Colditz was much more male-oriented. Boys of a certain age, who spent long hours playing Major Pat Reid's Escape from Colditz game, will be delighted by the overdue release of this exemplary series on DVD.

They already knew Guy Hamilton's The Colditz Story (1954) from afternoon screenings on sick days from school. But the 28 episodes transmitted by the BBC between 1972-74 brought German prisoner of war camp Oflag IV-C to life and enhanced its romantic reputation as an escape-proof bastion.

It's now clear why this was such a superior programme, as the writers included such luminaries as Ian and Troy Kennedy Martin, NJ Crisp, John Kruse, John Brason and Bryan Forbes, who had played Jimmy Winslow in the British Lion feature. But, at the time, it was the first-rate ensemble that made the stories so compelling.

Jack Hedley exuded dignified authority as the senior British officer, while Edward Hardwicke combined pluck with pragmatism as the head of the escape committee. David McCallum and Christopher Neame stood out among the supporting cast, which was periodically bolstered by such guest inmates as Robert Wagner, Dan O'Herlihy, Jeremy Kemp (who concocted an audacious scheme to fly a homemade glider off the castle roof) and Michael Bryant, who excelled as a wing commander who feigns madness in the hope of a compassionate release.

However, the Germans were just as memorable, with Bernard Hepton recalling Erich von Stroheim's gentlemanly Kommandant in Jean Renoir's La Grande Illusion (1937), while Hans Meyer combined steel with honour as his loyal Hauptman. But no one left a deeper impression than Anthony Valentine. He was truly terrifyingly malevolent as Major Horst Mohn, a former Luftwaffe ace who had served on Hitler's personal staff, and his sadistic delight in confounding meticulously planned schemes brought an extra frisson to the already tense escape episodes.

Co-produced by the BBC and Universal TV, the series boasted suitably cramped sets that reinforced the oppressive sense of enclosure. The shift between outdoor scenes shot on film and interiors recorded on videotape now seems a little cumbersome But the most impressive aspect of this estimable series was always the avoidance of caricature that had undermined so many British POW pictures in the immediate aftermath of the war.