And indeed, Unity Mitford, the tall, blonde daughter of an English aristocrat, had long been adding colour to her relationship with the leader of Nazi Germany, Adolf Hitler.

That she knew the F¸hrer, was part of his social circle and even one of his favourites, was not to be doubted.

She waited for him wherever he went, and eventually wormed her way into Hitler's life - "Wolf", as she called him in letters home, though never to his face.

He had come to like the company of this "Child" as he called her.

She amused him and was light relief in his life. He may even have thought, mistakenly, that, with her background, she might have some influence on British affairs.

He had found her the flat she had just taken possession of. It had belonged to Jews who had "gone abroad", she didn't know where, but it didn't take a genius to guess what this was a euphemism for.

She was virulently anti-Semitic anyway, so she didn't give a second thought to their fate.

It was her own fate that concerned her. She was wedded to the Nazi cause and now, in the late summer of 1939, with Britain and Germany on the brink of war, she was trapped.

She faced the prospect of being a traitor to her homeland or a traitor to her evil adopted cause.

The 25-year-old Unity had her only answer lying in the drawer of a writing table in the sitting room.

The day war was declared, she took out the silvered pistol, small and neat, the sort that nestled in the hand.

It was "a harlot's gun", according to a German woman in Hitler's entourage who disliked this intrusive English girl with her lip-sticked mouth and lowcut blouse.

Unity hurried to the English Garden in the centre of Munich, sat on a bench and shot herself in the head.

The bullet lodged in her brain but did not kill her.

But what had died was one of the most eccentric and unrequited romances of the 20th century.

Or had it? Because an article in the New Statesman magazine this week raises the sensational supposition that Unity Mitford returned to England in early January 1940 not on a stretcher as an irreversibly braindamaged patient but as a mother-to-be.

She was pregnant. And the father of her child? The F¸hrer himself.

Martin Bright, the magazine's respected political editor, tells how a few years ago he was contacted by a woman living in Oxfordshire who said that her aunt, a nurse, had run a "nursing home to the gentry" during the war and that Unity Mitford had been delivered of a baby there.

When asked who she thought the father was, the aunt had replied: "Well, she [Unity] always said it was Hitler's."

This putative baby of the otherwise childless F¸hrer was apparently given up for adoption, raising the prospect that somewhere in Britain today is the F¸hrer's 67-year-old love-child.

He would be the inheritor of some of the most extraordinary genes in history.

Bright was extremely sceptical - "this was either the scoop of the century or completely bonkers" - but he passed the story on to an executive of Channel 4, who leapt on the idea to turn into a documentary.

But there was no record of Unity being there, let alone a baby being born to her.

And nor could there be, according to Unity's sole surviving sister, Deborah, Duchess of Devonshire, last of the six famous Mitford girls whose rebellious exploits and outspoken opinions were headline news through the tumultuous 1930s and 1940s.

She dismisses the story outright.

"People should stop listening to village gossip," she told Bright.

But he feels certain that at the very least Unity was in that nursing home for a while, recovering, he thinks, from a nervous breakdown.

In which case, here is another mystery in the long-running Mitford saga.

Doubts have often been raised about Unity's return to this country.

Why was this acknowledged pro-Nazi allowed to go free? Why was she not prosecuted or interned like one of her other sisters, Diana, the wife of Blackshirt leader, Oswald Mosley?

There was a clamour for this in the newspapers at the time, and it has recently been revealed that MI5 wanted to detain and interrogate her.

It was on the unexplained orders of the Home Secretary himself that she was instead returned to her family, who cared for her until her death.

The question now being raised is whether this was all some elaborate cover-up for her pregnancy.

Certainly, Unity would have been happy to bear Hitler's child, preferably in wedlock rather than out of it.

She never disguised her wish to marry the F¸hrer.

In her over-imaginative mind, it was not just a romantic coupling but a political fusion of Great Britain and Greater Germany, for the betterment of mankind.

She adored Hitler. In letters to her sister, she described him as "the greatest man of all time".

The effect he had on her was physical. The first time she saw him, she trembled all over with excitement and had to put down a cup of chocolate she was holding.

Her love was blind. "Poor sweet F¸hrer," she said in another letter, "he's having such a dreadful time."

Which Hitler was, in a sense, having just butchered a large gang of old friends and supporters, ordering them to be dragged from their beds and shot in the Night Of The Long Knives.

But the brutality of the regime and the man himself made no impact on Unity.

"Best love & Heil Hitler!" she signed off all her letters.

All of which alarmed some of her sisters. They had always seen "Birdy", as they called her (also "Bobo" and "Boud"), as charming if a little odd, but "full of gaiety" in sister Nancy's words, and hugely funny according to Deborah.

Yet she was caught up in a personal crusade that would be the death of her.

But the idea of a sexual relationship with Hitler does not stack up. For one thing, the F¸hrer's libido was slight to the point of non- existence.

Other dictators were notorious for their promiscuity. Stalin was rapacious.

Hitler, destroyer of nations, was wary of women, though they flocked to his presence and were turned on by his charisma.

He had his mistress, Eva Braun, though she complained she hardly ever saw him.

Eva had some girly concerns about Unity being in Hitler's presence so often, but the two of them were almost never left alone at their meetings.

And when they were, it was Unity's turn to complain that his aides were always interrupting.

The idea that she slept with Hitler was "absolute nonsense", according to one of his adjutants.

The fact is that the Nazi old guard and the SS detail around him were suspicious of Unity, unable to fathom what this large, Valkyrie-like Englishwoman was up to and why Hitler tolerated her.

Some suspected her, wrongly, of being a spy when, in fact, she was simply smitten.

Winifred Wagner, daughter-in-law of the composer Richard Wagner, and one of the social set around Hitler, declared that marriage to Unity was quite impossible.

"She might have hoped for it, he was kind and polite, they got on well together, but he used to say he could never marry anyone."

And anyway, Frau Wagner added, Unity "just wasn't interesting enough".

It was a reaction that others had on seeing her. One Englishman who saw her clicking her heels and saying "Heil Hitler" couldn't stop himself giggling.

Her sisters, too, mocked her as Mrs "Wessel", the storm-trooper killed by communists and immortalised in a Nazi marching song.

Unity took no notice. Her heart still fluttered when she saw Hitler's car drive by - "I stood saluting. When I got to the hairdresser I felt quite faint & my knees were giving, you know how one does when one sees him unexpectedly."

But the passion was all one-sided. Elmar Streicher, the son of Julius Streicher, the sadistic and psychopathic gauleiter hanged at Nuremberg, knew Unity.

"She had nothing to do with Hitler as a woman," he said, "she was just a butterfly to a flower. As a woman she was so very tall, you had to laugh to see it. She simply wasn't sexy. She was a virgin to the day of her death, I'd put my hand in the fire to say that."

If there was no sex, there could be no son of Adolf. Not then, or now.

But Streicher may have been wrong about Unity. There were rumours that she slept with SS officers. Could

she indeed have been pregnant when she was brought home in 1940, but by someone other than her beloved F¸hrer?

This is unlikely. In the tens of thousands of letters written by the six Mitford sisters both to each other and to those outside the family, there is not even the slightest hint of Unity being with child or a nephew being born.

Perhaps their letters were self- censored to conceal this great secret. But again, that seems unlikely.

The Mitfords were the world's greatest gossips. Between them they had in-roads into every conceivable social circle - literary, political, aristocratic and so on: and yet not a word, not even an ambiguity, can be detected to suggest that this was the dread family skeleton.

Certainly, the girls and their mother were very protective of Unity when they got her home. But that is hardly surprising.

After she shot herself in Munich, she lay unconscious in hospital for weeks - during which time no news of her suicide attempt reached Britain.

Hitler had banned the German press from reporting it, and speculation in England was that she was probably in a concentration camp.

Nancy, sitting in an air-raid shelter in anticipation of an imminent gas attack, thought that would be poetic justice, but concerned for Unity, nonetheless wrote to her sister, Jessica: "Poor Boud. Fleet Street says she has been put on a farm for Czech women.

"We have written to the Duchess of Aosta to ask the Italian consul in Munich to find out what has really happened, & if she is awfully miserable perhaps she could go to Italy.

"Probably she is on top of the world though."

Unity was far from that, though she was safe. Her beloved F¸hrer did the decent thing by this strange, obsessed Englishwoman who had been his fervent and unquestioning admirer for so long.

He had her treated in Germany before being taken by train to a clinic in neutral Switzerland, where, in January 1940, "Muv" and sister Deborah came to fetch her.

They found her paralysed and seriously ill, with her hair still matted from the day she tried to shoot herself.

She returned to England on a stretcher, the Press clamouring for pictures as she came off the cross-Channel ferry at Folkestone.

Could she really have been hiding a seven-month bump beneath the blanket? It was a long time since she had actually been alone with Hitler.

In the months before the war, she had found it almost impossible to get through his SS screen.

In Britain, some papers wanted her scalp. The Daily Mirror wondered why "the Mitford girl, who has been openly consorting with the King's enemies, should go scot free".

But taking revenge on her would have been pointless. The bullet, still in her brain, fuddled her memory - "a mercy, I expect," said Nancy.

All she could recall was that Hitler once said she had nice legs. She told her sisters she was glad to be home: "I thought you all hated me but I don't remember why."

She was left with the mental age of a 12-year-old, and was unpredictable, fractious, clumsy and incontinent at night.

She replaced her obsession with Hitler with an obsession with religion.

Her mother took on the task of caring for her for the rest of her life.

Perhaps she did have a nervous breakdown and spent a little time in a nursing home near her mother's cottage.

After all she had been through, it would hardly be surprising if she needed professional help or her mother some respite.

But as for giving birth to a child, that seems simply unbelievable.

Unity died in 1948 of meningitis and "an old gunshot wound", according to her death certificate.

Her sisters, even those who deplored her politics and hated her association with Hitler, mourned her deeply.