The welcome from the Duke of Marlborough could not have been warmer. Blenheim Palace may be steeped in the nation’s history but the 89-year-old baroness was about to bring the past alive as no other surviving member of the Churchill family could.

Mary Soames, the youngest and only surviving child of Winston and Clementine Churchill, once produced a compelling biography of her mother.

But on Sunday she returned to her father’s birthplace to tell A Daughter’s Tale, to borrow the title of her long-awaited memoir published this month, based heavily on her diary and family letters.

At the Independent Woodstock Literary Festival, where she spoke to a packed audience in the palace’s Orangery, she told of her encounters with Stalin and General de Gaulle, her memories of wartime service in the mixed anti-aircraft batteries and a childhood played out in her own Garden of Eden, Chartwell, her family’s home in Kent.

But mostly she spoke of what it was like to be the daughter of one of the greatest men of the 20th century.

Like many of her audience, she explained that during the war years she came to hero worship her father.

“I started to see how other people regarded my father, and naturally that had an effect on me,” she told the historian Philip Ziegler, who conducted the interview before questions from the floor. “I suddenly realised people looked at my father in quite a different way. They relied on him.”

She was 17 when the Second World War broke out, but her vivid memories extend to long before then.

When her parents moved into 11 Downing Street, on Churchill’s appointment as Chancellor of the Exchequer in 1924, she readily recalled being scolded for pouring water from a window on to the head of a police officer standing outside the front door.

“I was tremendously loved and spoilt. One of the people I remember most was Lawrence of Arabia who came to Chartwell, in the days when he had changed his name to Aircraftman Shaw. He would arrive with a great roar on his motorcycle.

“One day when he was staying my father told me to come downstairs in my dressing gown before dinner because there was a surprise for me. And there was my friend in the robes of a Prince of Arabia. It was something I’ve never forgotten.”

In her book she reveals that her relationship was easier with her father than Clementine, with both parents often absent. “The development of a closer relationship between my mother and myself was not always equable; there were tempestuous passages between us. I sometimes found her difficult to understand and extremely demanding. I dreaded her displeasure and emotional electric storms that could brew up.”

Her father shared his daughter’s love of animals. But his study and bedroom, where he often worked, were no-go areas. “No noise — whistling particularly was abhorred — outside papa’s study was permitted. A thunderous roar of rebuke and reproach would result from any infraction of this not unreasonable rule.”

Her elder siblings, Diana and Randolph, were remote figures during her teenage years, with Randolph briefly at Oxford University.

“Randolph’s spasmodic visits to Chartwell became always associated in my mind with shouting, banging doors and rows: I tended to keep out of the way.”

Her father would take his youngest child to visit friends such as David Lloyd George.

“I was immediately struck by the great man’s white locks, his animation and his celebrated Celtic charm.”

Many years later she joined her father on one of his meetings with the Russian dictator.

“Stalin was much smaller than I thought he was going to be. He had a most beautiful uniform — cream serge material. It was most elegant. He had the most twinkly eyes.

”My father received news of the death of a great friend while they were together. Stalin told him, ‘the death of an individual is always a tragedy — with millions it’s just a statistic’.”

Against a background of cataclysmic events, she confessed to still being able to continue a life packed with family, social and romantic events during the war.

“I remember when I looked back at my diaries that we once arrived to dance at the Cafe de Paris and found ambulances and fire brigades and that it had been blown up — so we went to find somewhere else to dance. That shocks me deeply now. Young people always want to have fun.

“Looking through the diaries, it was sometimes pretty embarrassing. I often felt like writing in square bracket: ‘oh Mary, really!’”

Fears that Chequers might be targeted by Nazi bombers resulted in Ditchley, in Oxfordshire, becoming a regular weekend retreat for the Churchills during the war years.

Lady Soames would travel by train to Oxford before heading to the grand house, just down the road from Blenheim. Ditchley was to be the scene of one of the great dramas of her life, showing how her private life was conducted against a background of earth-shaking events.

Much to her parents’ displeasure she had become engaged to Eric Duncannon, an officer in a county regiment whom she had met at an RAF dance. Her mother demanded that the wedding was put off.

“She perceived, rightly, that I was not in love with Eric and determined to do everything in her power to stop the whole affair,” recalled Lady Soames in her book.

Feeling unable to distract Winston from the war, Clementine commandeered President Roosevelt’s representative, Averell Harriman, to take her for a walk in the grounds, while her mother went to break the news that the wedding was off to the distraught Eric.

In the midst of the romantic crisis came news that Rudolf Hess, the deputy leader of the Nazi Party, had flown to Britain, landing by parachute near Glasgow.

“So mountains and molehills acquired their proper proportions,” she now ruefully reflects.

After the war she would marry Captain Christopher Soames, later Lord Soames, with whom she would have five children. Her husband died in 1987.

A short but sturdy woman, with a voice not dissimilar to the Queen’s, like the monarch Lady Soames shows few signs of frailty, managing without help to ascend a steep flight of stairs to the festival green room.

After listening to her entertaining the duke and hundreds of others in the Orangery for over an hour, many doubtless left reflecting on the irony of what she revealed to be an abiding fear.

It turned out to have nothing to do with Nazi bombers or the prospect of being taken prisoner after a German invasion.“You know, I was always afraid of boring my father,” she said. “It was always a great treat arriving home but I just didn’t want to bore him.”

  • The Daughter’s Tale by Mary Soames is published by Doubleday (£25).