The wife of George Osborne, the shadow chancellor, has revealed her fascination for a relative whose sexual escapades once scandalised British society.

Frances Osborne says that she considers her great-grandmother Idina Sackville, daughter of the Earl De La Warr, to be an inspiration, despite her louche and dissolute life at the centre of the notorious Happy Valley colonial set in prewar Kenya.

Sackville, who was married and divorced five times and held partner-swapping parties at her African ranch, shocked 1930s Britain when news of her behaviour became public.

One of Sackville’s husbands was Josslyn Hay, the womanising Earl of Erroll, whose mysterious murder in 1941 was later immortalised in the film White Mischief.

Yet Osborne, rather than being perturbed when she learnt as a girl of her connection to the errant aristocrat, found the opposite to be the case and admired Sackville’s joie de vivre.

“I was a clever, swotty girl and Idina gave me the confidence to dare to be something more,” she said.

Osborne, who has now written a book about Sackville entitled The Bolter which is serialised today in The Sunday Times, said her family had kept the identity of her great-grandmother secret during her childhood for fear of her being seen as a role model.

When she was finally told – following the publication of the book White Mischief in 1982, which described Sackville’s life in detail – Osborne found herself compelled to find out more.

She writes: “I was 13 years old and transfixed. Was this the secret to being irresistible to men, to behave as this woman did? My mother had been right to be cautious: Idina and her blackened reputation glistened before me.”

So notorious was Sackville’s appetite for sex and her reputation as a serial divorcée that she was fictionalised by Nancy Mitford as a character in her books The Pursuit of Love, Love in a Cold Climate and Don’t Tell Alfred.

The apogee of the Happy Valley set’s infamy came following Hay’s murder. He had been having an affair with Diana, the young wife of Sir Jock Broughton, who was tried for the murder but acquitted, although he later committed suicide.

Despite having abandoned her first husband with their two young sons, one of whom was Osborne’s grandfather David Wallace, some remember Sackville for having an intrinsic kindness.

When Wallace was killed during the second world war, Sackville wrote to his widow: “There is so little I can say, for what are words when one has lost all one loves.”

On becoming a mother herself, Osborne saw Sackville’s abandonment of her children in a new light, but her fascination with her great-grandmother continued.

She writes: “Idina, the person whom I yearned most to meet in an afterlife, had, according to my mother, done something that now made me feel quite sick. But Idina was beneath my skin.”

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