Elizabeth Longford was matriarch of the most powerful and well-connected literary dynasty in the land — that of the Pakenhams, Frasers, Pinters and Billingtons — and her life was spent among intellectuals for whom the production of books of all kinds was at least as natural as the production of children. Her own historical writings combined erudition and thorough research with wide appeal. As Countess of Longford, wife of the 7th Earl (Frank Pakenham), she was a notable crusader in society and in Labour politics for many a losing cause.

It was a grand and indomitable life, which has already been the subject of a biography. In her early years she occasionally overlapped with the Bloomsbury Group, and her own clan has some of the same fascination. Like them, the Longford family are pillars of the left wing of the Establishment, and sure enough, Elizabeth Longford kept a diary and encouraged all her children to do the same. Longford thinking was progressive, though always sensibly, never militantly so, yet their life perfectly represented the conservatism of comfort, divided as it was between Chelsea in the week and an 18th-century house at Hurst Green, East Sussex, at weekends.

Elizabeth was the daughter of N. B.Harman, a Unitarian Harley Street ophthalmic surgeon, and Katherine Chamberlain, a niece of Joseph Chamberlain; she was thus a second cousin of Austen and Neville. She was educated at Headington School, Oxford, where her main talent was thought to be drawing, though she wrote a Gothic novel at 13 and dreamt of becoming an actress. But her mother was a determined proponent of proper education for girls, so she applied to Oxford. Rejection stiffened her resolve: she took coaching for a year and applied again, winning a place at Lady Margaret Hall.

There she was regarded as one of the cleverest and most attractive women undergraduates of the day. She became a friend of W. H. Auden, Stephen Spender, John Betjeman and David Cecil — and Quintin Hogg later said: “There was not an undergraduate in Oxford who wouldn’t have considered it a privilege to hold an umbrella over her head.”

She received five proposals of marriage. Two were from her tutors, Maurice Bowra, who persuaded her to switch from English to Greats, and Hugh Gaitskell, who had a considerable effect on her left-liberal convictions. After going down — without the expected first, perhaps because a friend of hers had just been killed in an accident — she spent six years lecturing in English, politics and economics for the Workers’ Educational Association.

Gaitskell was instrumental in her social as well as her socialist development. In 1927 he took her to Magdalen College ball, at which she first glimpsed Frank Pakenham. The following evening, at the New College ball, she saw him again, and kissed him. Yet it was four years before they married, and she remembered that in a year’s courtship while they were at Oxford, she never invited him to anything on his own.

When they married he was a committed Conservative, working for the party. Nevertheless she stood unsuccessfully as Labour candidate for Cheltenham in 1935. She was subsequently Labour’s candidate for King’s Norton, Birmingham, until 1943, and stood for Oxford City in 1950. She was never elected, but she did make one convert, her husband joining the party in 1936.

Conversely, she became a Roman Catholic in 1946, six years after her husband had converted without telling her. She was won over by reading Evelyn Waugh’s biography of Edmund Campion, not knowing that Waugh had opposed her marriage — as became apparent when his letters were published.

Frank Pakenham’s political career began in earnest after he resigned his commission because of ill-health in 1940. He soon became personal assistant to William Beveridge, and from 1948 to 1951 he was Minister for Aviation. For six months he was First Lord of the Admiralty, and by 1964 he was Leader of the House of Lords. He went on to campaign against pornography and for penal reform and clemency in several high-profile cases; “hate the sin, love the sinner” was his maxim. For 60 years he was also a prolific, didactic author.

Meanwhile, the Longfords had four sons and four daughters in quick succession, claiming to be able to determine their sex by attention to the body chemistry. It was a most extraordinarily energetic and driven family. “When there were eight of them at home with all their activities and high spirits and me being so ambitious,” she said, “we were all very competitive and quarrelsome. I transferred the intellectual snobbery on to the children and pushed the eldest ones too much.”

On the other hand, she felt that too many parents nowadays abandon their responsibility towards their children when they reach their teens, out of misplaced regard for their independence when they are still too young to know how to exercise it.

The Labour Party took exception to a potential MP having so many children, and when the choice came, she put family first without much regret. As it turned out, her metier was not politics but writing, which she began to do at the behest of newspapers wanting her to dispense advice on family life.

She produced some excellent historical books and a fine volume of memoirs, although she turned out potboilers too. Yet it was not until she was in her fifties that she published her first book, Jameson’s Raid (1960). This was at the time the best account of that controversial episode of 1895-96, although later investigations and C. M. Woodhouse’s publication of the famous “missing telegrams” in his life of Cecil Rhodes suggested that Joseph Chamberlain was more deeply involved than she had believed.