Lady Falkender, who has died at 86, was one of the most influential and bizarre political figures of the Harold Wilson era.
Formerly Marcia Williams, she enjoyed a stormy power partnership with the Huddersfield-born Labour prime minister. It was one of the most famous and mysterious relationships in modern political history.
The uncanny influence she exercised over Mr Wilson, and over his decisions, frightened many MPs and was widely resented in Whitehall.
Often, it appeared from the outside, Mr Wilson would submit meekly to her demands. Occasionally, to the horror of his more conventional aides, she would shout and scream at him, treating him like a small boy.
However, as she daily gained more influence and power at 10 Downing Street, so she was more and more exhilarated by the pace of life at the centre and relished her skirmishes and victories over those jealous of her astonishing position.
The press, eager to establish a romantic relationship, failed to discover anything more intimate than a passionate political rapport between them.
However, a sensational claim that the pair had an affair was made in a book published in 2002 by Joe Haines, who was the then Prime Minister’s press secretary.
Haines reported that, in 1972, Marcia summoned Mr Wilson’s wife Mary and bluntly told her of the alleged fling.
She is reported to have told the astonished Mrs Wilson: “I have only one thing to say to you. I went to bed with your husband six times in 1956 and it was not satisfactory.”
The story became even more bizarre. There was, Haines recorded, growing unease among the prime minister’s closest advisers as she repeatedly told her colleagues that it would take just one telephone call to end Mr Wilson’s career.
Marcia, who consistently denied having had a sexual relationship with Mr Wilson, made many enemies in Downing Street and Whitehall, but those who crossed her, and had flaming rows with her, invariably came off worse, even if they had won the argument.
This was largely because Mr Wilson always took her side in every dispute, whether she was in the right or the wrong. She was a daunting woman and you trifled with her at your peril.
One of the memorable highlights of her career was Mr Wilson’s celebrated and controversial resignation honours list which included, among other unlikely names, the manufacturer of his Gannex raincoats, Sir Joseph Kagan, who ran a mill at Elland, near Halifax, and was soon to be prosecuted and jailed over his tax affairs.
It was discovered subsequently that some of the names had been scribbled on lavender-coloured notepaper – the so-called Lavender List – in Marcia’s handwriting, leading to the suspicion that she had been responsible for it.
However, it was pointed out that secretaries often set down in writing the dictated thoughts of their employers.
Another strange feature of her life was a long-lasting affair with the late Walter Terry, one-time political editor of the Daily Mail.
Terry was Mr Wilson’s favourite political reporter and was a leading member of the so-called White Commonwealth which the prime minister set up, involving a few handpicked lobby journalists.
The liaison between Marcia and Terry produced two sons. It was the only time she was in love. Once she said: “I do have lovely romantic dreams about how life might have been. I envy couples.”
The so-called Duchess of Downing Street was born in March 1932, and educated at Northampton High School and Queen Mary College, University of London.
Her marriage to George Williams foundered after five years: he wanted to live and work in America and she did not.
She was private and political secretary to Mr Wilson over a period spanning from 1956 to 1983.
Marcia played a big part in the Wilson family life. Mary, who bore an intense dislike to political life, finally recognised that Marcia had staked her claim on territory that she herself had no wish to occupy.
Equally, Marcia came to appreciate that Mary was the solid foundation on which Mr Wilson’s life was built. In a distant sort of way, therefore, they complemented one another.
She blamed the Labour leadership for not pushing more women to the top. Once she said: “Many leading Labour figures have an attitude to women’s rights completely opposed to the whole spirit of a movement that believes expressly in equal opportunity.”
In her memoirs, Downing Street In Perspective, Lady Falkender described how the Labour leadership laughed in derision the day Margaret Thatcher became Conservative leader in 1975.
She wrote: “They were all laughing, joking and slapping each other on the shoulders with remarks to the effect that all was now well. How could, they were asking, the Tories possibly win with a woman at the head?”
Only the prescient Mr Wilson and Peter Shore provided the cautionary and dissenting voices.
Marcia became a life peeress in 1974, commenting later: “My peerage has been a great problem to me because I have never known how to handle it. But now I know myself pretty well. And I think if the press has got me wrong there is nothing I can do to put it right.”