Elizabeth Longford, who died on Wednesday, aged 96, was matriarch of a large dynasty that almost equalled that of Queen Victoria (one of her biographical subjects) in size. She was endowed with gifts of beauty and charm to which she added the virtues of industriousness and a sympathetic curiosity about other people.
Born Elizabeth Harman on Harley Street, London, the eldest of five children of two doctors, she had the archetypal Edwardian London childhood: nannied and privileged, and punctuated by visits to her mother's uncle in Birmingham, Joseph Chamberlain, the Victorian statesman.
At Francis Holland School in London, and Headington School in Oxford, she won all the prizes, but it was at Lady Margaret Hall, Oxford, that she blossomed into "one of the aesthetes' molls" (in John Betjeman's words) whose social success was spectacular.
She was pursued by Hugh Gaitskell and the Oxford don Maurice Bowra (she was the only girl at his parties) and was a friend of Evelyn Waugh and Lord David Cecil. Quintin Hogg, later Lord Hailsham, said that "there was not an undergraduate who would not consider it a privilege to hold an umbrella over her".
But one night at the end of a New College ball her gaze alighted on the slumbering form of Frank Pakenham - "like a Greek god", she said, "with brown curls".
She bestowed a kiss on the brow that was later to be instantly recognised by its conspicuous high dome, a gift to caricaturists.
They were married at St Margaret's, Westminster, in 1931, family legend being that Frank turned up at Westminster Abbey by mistake, to find it empty, and was consoled by his best man Freddie Birkenhead saying: "Nobody goes to weddings these days."
Her bridegroom introduced her to the Workers' Educational Association, for whom she became a tutor, and she introduced him (a Tory in youth) to socialism. Later, when he converted to Catholicism and received instruction secretly in Farm Street (to her distress), she followed him.
Since child number seven had already been born at that stage, she never followed the Pope's edict on contraception. She had been an early disciple of the gynaecologist and birth control pioneer Dr Helena Wright, who had instructed her on how to ensure an equal number of daughters and sons by the judicious use of alkaline douches. But it was her "addiction to motherhood" which effectively scuppered her political career. She had first stood for Labour in Cheltenham in 1935, and then nursed the safe seat of Birmingham King's Norton until 1944, when a faction in the constituency party expressed its dismay over her sixth pregnancy. She stayed on, but later reflected that if her husband did not win in Oxford, she could not see him keeping the home fires burning while she set the Thames alight at Westminster, and resigned her candidacy. A year later the seat was won with a 12,000 majority; her compensation was two more children. She became a government wife, since Frank Pakenham (Lord Longford after 1961) held various posts in the Attlee and Wilson cabinets. She did stand once more for Oxford in 1950 (probably the only mother of eight to fight an election) to discharge, she said, her political debt. She remained loyal to the Labour Party; her niece is the current British government minister Harriet Harman.
Her writing career began because she was so often telephoned by journalists for advice on parenthood that Lord Beaverbrook gave her a column in the Sunday Express in the 1950s.
Beaverbrook told her that those who practised "the black art" (journalism) could never escape it, but her husband steered her towards books, first on trivial subjects like children's parties, then on larger subjects, the more daunting the better. She was over 50 when she wrote Jameson's Raid (1960), followed in 1964 by Victoria RI, her first bestseller and winner of the James Tait Black prize (she had the advantage of access to the royal archives) and her acclaimed two-volume life of Wellington (1969 and 1972).
She was keen on research, relished travelling to visit battlefields and passed on her passion for historical biography to her eldest daughter Antonia Fraser (the idea of writing about Mary Queen of Scots was originally Elizabeth's), to her eldest son Thomas and to various grandchildren whom she always advised: "Not to study history would be like living in a house with no windows."
Publishers demanded biographies and picture-books, which she diligently supplied at an age when others contemplate retirement: a life of Churchill, a history of the house of Windsor, Byron's Greece, eminent Victorian women, lives of the Queen and the Queen Mother, and a collection of the letters of Queen Victoria to her daughter Louise, Darling Loosy (1991).
Her last substantial biography (apart from her own autobiography, The Pebbled Shore, in 1986) was of Wilfred Scawen Blunt (1979), a figure she wrested from poetry anthologies and fleshed out, at somewhat exhausting length, into a full-blooded and Byronic character.
The year 1969 was a glittering one for the family, with five of them producing books, feted collectively at a Foyles luncheon.
But that summer was a dark one: while Elizabeth was visiting her diplomat son in Warsaw, her youngest daughter Catherine was killed in a car crash. In her memory a prize for young women journalists was set up, won in its early years by the Guardian's Polly Toynbee, Tina Brown and Sally Beauman, and still a fertile source of youthful talent.
Domestic life was not of great interest to her - the family claimed that she had never changed a nappy - but she found her children enormously rewarding, and brought great skill and wisdom to the grandmotherly role, welcoming her enormous and expanding family, in segments, at Bernhurst, the Sussex house bequeathed to her husband by a Longford uncle. Here the proceeds of her biographies supplied a swimming pool where Elizabeth maintained her girlish figure into her 80s with 20 stately lengths each day.
The Longfords' more natural habitat was metropolitan, since they shone at gatherings where each would dart about independently, asking questions, always enthralled by the vagaries of political life.
They often took guests to lunch at the House of Lords, particularly those who had been checked by misfortune, and Harold Macmillan when he was looking a bit forlorn.
When she wrote Royal Throne in 1993, she had thought that a book subtitled "the future of the monarchy" would be a pleasant occupation for her 87th year: in the event, it fell precisely into the Queen's annus horribilis, and Lady Longford had to rewrite her final chapter after the formal separation of the Prince and Princess of Wales.
In it she declared her staunchly monarchist faith in Prince Charles, who had granted her a long interview for the book, as a future king without a queen.
Elizabeth Longford's life-enhancing vitality expressed itself in her eager attentiveness to anyone she was talking to. She seemed to have read every book and every newspaper, and even when her eyesight failed in recent years, a willing band of volunteers would read the newspapers to her every day.
"I think it would be very difficult to become bored with Elizabeth," Lord Longford said. "No one else has ever been." At Frank's funeral wake she sat like Queen Victoria in a lacy cap, and told amusing stories of his boyhood.
Within the last year she published new versions of her Queen Victoria and Wellington biographies. She attended the Queen Mother's memorial service and in June this year took part in a memorable Desert Island Discs on BBC Radio 4, choosing predominantly hymns. Her chosen luxury was a miniature orange tree.
When Isis, the undergraduate journal, made her one of its early female idols in 1930, they described her as "artistic, beautiful, cultured, decorative, enigmatic, fashionable, girlish, sometimes headstrong" and hoped she would "live long, in the great tradition of British women", as indeed she did.
Her final wish was to be taken from her London nursing home to Bernhurst, where she retreated to her feather bed, with a great tulip tree at the window, and slipped away peacefully, surrounded by her family.
She is survived by four sons and three daughters, including the writers Thomas Pakenham, Antonia Fraser, Rachel Billington and Judith Kazantzis, 26 grandchildren and seven great-grandchildren.
Elizabeth Pakenham, Lady Longford: born August 30th, 1906; died October 23rd, 2002