Was Winston Churchill unfaithful to his wife Clementine?

The documentary takes us to an extraordinary time in 1930s Britain, with Winston in his “wilderness” years – out of power and with his warnings about Adolf Hitler largely unheeded by the establishment and government of the time – and partying in the South of France.

He was especially fond of Chateau de l’Horizon a palatial pile on the French Riviera owned by actress and socialite Maxine Elliott, and it was there he hung around with Lady Castlerosse in the mid-1930s. And, according to newly discovered testimony from a key witness who has just come forward (as well as surviving members of her family), their affair lasted for a period of around four years.

And why does it matter? The programme wants us to believe that this isn’t just prurient title tattle, but a story about how Britain’s war effort could have been derailed….

Who was Lady Castlerosse?

She was born Doris Delevingne in 1900 and married Viscount Castlerosse in 1928, though the marriage was in effect over the following year.

Lady Castlerosse was, as her biographer says, an "expert philanderer" who essentially lived off wealthy men – not a damning judgement the programmes makes, merely the reality for her and many women of her class at the time. But the mind-set of Lady Castlerosse, who once said that there was “no such thing as an impotent man, only an incompetent woman” is intriguing. And also, when one considers how her life panned out (see below), rather sad.

But she was dazzling in her prime, and possessed what were known at the time as "racehorse legs". She had an affair with society photographer Cecil Beaton – even though he was gay – and clearly enraptured Winston Churchill who painted three portraits of her (and only one of his wife) during his life.

She also happens to be the great-aunt of the model and actress Cara Delevingne...

How has the reputed affair now come to light?

The truth emerges in three sentences recorded by Churchill’s aide, John “Jock” Colville, two years before he died in 1987. Colville was assistant private secretary to three prime ministers: Neville Chamberlain, Churchill and Clement Attlee. He was also private secretary to Princess Elizabeth, now the Queen, from 1947 to 1949. Colville made a recording in 1985 for the Churchill archives at Churchill College, Cambridge, but it appears no historian or biographer listened to the entire tape — until now.

“He [Churchill] did one terrible thing,” Colville says. “He was not highly sexed and I don’t think he ever slipped up, except the once. He had a brief affair with Doris Castlerosse.”

Who else believes it happened?

“My parents talked about the [Churchill] affair; we knew about it,” says Castlerosse’s niece, Caroline Delevingne, in the documentary.

Letters from Churchill to Castlerosse include one from 1933, when he wrote: “What fun we had at Maxine’s. I wonder shall we meet again next summer.”

Churchill stayed with Castlerosse at Elliott’s house over the next three summers, each time without his wife. By early 1937, Castlerosse had moved to Berkeley Square in central London, where, according to Caroline Delevingne, “Winston would come to the house, while the staff were told to leave”.

Why is it historically important?

The programme says the affair began in 1933 in the Chateau de l’Horizon in the south of France and ended in 1937.

The timeline means it was before Churchill became Prime Minister but they did meet at least once when he was wartime leader – in the US, where Lady Castlerosse was an unhappy exile living in New York in 1942. There she soon ran out of money and it was feared the affair could expose Britain’s wartime leader to blackmail.

So in 1942 he secured her passage home – quite an ask considering the war was on – and was deeply concerned about a painting of his of her that she had in her possession and that was rather suggestive.

If news leaked in the US that Britain’s great wartime leader had been unfaithful to his American wife, US sympathy for the Allied cause could have waned considerably, the thinking goes, and the Second World War may have had a different outcome.

It’s a fanciful and slightly far-fetched notion that of course never came to pass. What is probably more interesting is the human story it uncovers – the fact that there were cracks in the Winston/Clementine marriage before the war. And the world of pre-war opulence is a fascinating one as well.

Did Clementine know? Did she ever stray?

Clementine, who herself had a brief relationship, in 1934, with Terence Philip, an art dealer, is said to have found out about her husband’s affair in the early 1960s. The programme claims that Clementine was shocked – and very upset – to discover the news and reportedly burnt some of the lovers’ letters.

What happened to Lady Castlerosse in the end?

She never met Churchill again after her return to London in 1942. She stayed at the Dorchester Hotel for two months before being found dead after an overdose of sleeping tablets. The programme assumes it was accidental, but the truth about that is never likely to be known...

Churchill’s Secret Affair is on Channel 4 on Sunday 4th March at 8pm