Barbara Castle, who has died aged 91, was Labour's Red Queen, the woman Michael Foot called "the best socialist minister we've ever had". Clever, sexy and single-minded, author of some of the best political diaries of her time, she was the most important female politician the Labour movement has yet produced, a unique witness to, and participant in, the 20th-century history of the left.
From the prewar unity campaign against fascism, via the early issues of Tribune, to the Bevanites in the 1950s, taking in Cyprus and the Hola camps in Kenya, and climaxing in the heart of Harold Wilson's government, she was an unflagging champion of an ethical socialism that she believed should shape every aspect of life. In one of the ironies of politics, she paved the way for Margaret Thatcher to capture the commanding heights of government.
Throughout her political career, Castle maintained a hard-headed pragmatism, without compromising a passionate belief in the transforming power of socialism. Her ambition, she said, was "to inch people towards a more civilised society". She was brave and determined, the heart-throb of the constituency Labour parties for nearly 30 years.
Her career foundered on an inability to master the key political skill of building support where it counted, in the parliamentary party. She claimed to find making political alliances demeaning; her critics found her wearisomely egocentric. Even her friends distrusted her temper.
The last five years brought her an Indian summer of popular favour, as her distaste for Blairism made her the heroine of the same right-wing press that had cheered her departure from the cabinet in 1976.
Barbara Anne Betts grew up in the secure environment of a family with a need for belief. The socialism of the Independent Labour party (ILP) was the main, but not the only, religion of the household. Her mother Annie, a Labour councillor, was a devotee of the romantic William Morris; her father, Frank, a tax inspector, was a poetry-writing intellectual who filled the columns of the ILP journal, the Pioneer, which he edited in the late 1920s and early 30s - with art, criticism and politics in equal measure.
He nurtured young talent like Vic Feather, thus enabling the future TUC general secretary to dismiss Barbara, when she was secretary of state for employment and productivity - fighting her doomed battle for trade union reform - as "a lass he knew when she was still in dirty knickers".
Although she was never untruthful about her own past, it was rather less proletarian than she would have liked for a party suspicious of middle-class intellectuals. She toiled through Bradford girls' grammar school, and followed her older, more brilliant, sister Marjorie to St Hugh's College, Oxford, where she made the daring choice of sex and practical politics over economics and philosophy. She graduated with a third-class degree and a sense of intellectual inadequacy, which drove her to work with almost damaging diligence throughout her political career.
She was determined to become a journalist and a politician, but the depression forced her to briefly earn a living selling dried fruit from a mobile display in a Manchester store while, in her free time, setting out to save the Labour party from the betrayal of Ramsay MacDonald's national government.
Soon after Oxford, Barbara fell in love with the leading socialist intellectual and journalist, William Mellor. He was married with a young child, but, for more than 10 years, they pursued a tempestuous, semi-public affair, their passion spent equally between each other and the politics of the left. But although she knew of the affair, Mellor could never bring himself to leave his wife. He died, suddenly, in 1942.
Barbara found other friends, notably her immediate junior at Oxford, Michael Foot. Later, he happily indicated they had shared more than Marx and Dickens in front of the gas fire of a small flat in Bloomsbury, but she angrily denied there had ever been an affair, and Foot, professing mild surprise, loyally retracted. Together, in 1937, they helped launch Tribune, which was edited by Mellor until he fell out with Tribune's financial backer, Sir Stafford Cripps.
The paper, whose declared mission was to recreate Labour as a truly socialist party, was also Cripps' personal contribution to the left's campaign against rearmament, and in favour of a united front against fascism. It was soon in conflict with the leadership, which, in turn, was increasingly making common cause with the Churchill wing of the Conservative party. Cripps sent Barbara off to Moscow, from where she reported, without irony, on the new assurance of Russian women in the age of Stalin.
Determined that not even war would interrupt her pursuit of a political career, she rejected more exotic offers, to became a temporary civil servant while she hunted for a parliamentary seat. In 1943, she made her first speech to the Labour party conference, accusing the leadership - accurately - of preparing to compromise on the timing of the implementation of the Beveridge report. "We want jam today, not jam tomorrow," she warned.
It was a popular cry on the Daily Mirror. Its night editor was Ted Castle: he put the story on the front page. After a courtship of proselytising together for Beveridge, on street corners and in parish halls, they were married - and stayed so, through some rough times, for 34 years.
In 1944, after a mutiny by Labour women who insisted that at least one woman candidate be interviewed, Barbara was selected for one of the two Blackburn seats, beating three men for a constituency she represented until her retirement from the Commons in 1979.
As soon as she got to Westminster, Cripps asked her to become one of his parliamentary aides. Clement Attlee notoriously underpromoted young and leftwing politicians, and, when Cripps moved on from the Board of Trade to take over as chancellor, Castle was left behind to work for his successor, Harold Wilson. She often disapproved of Wilson's rapacious ambition, but it was the start of the most important political relationship in her life. She nominated him for the leadership when he challenged Hugh Gaitskell unsuccessfully in 1960, and again when he won, after Gaitskell's death, in 1963.
When Labour was finally returned to power in 1964, her reputation was for division within the party, and personal vituperation against enemies outside it. Probably the only leader who would still have given her a department to run was her old friend Wilson. He squeezed her in to his first cabinet at the Department of Overseas Development - a department whose creation she had often advocated - and gave her the opportunity to reinvent herself, at the age of 53, as one of the most effective cabinet ministers of her generation.
With no ministerial experience, and a department to be chiselled from the stoney faces of the foreign, colonial and commonwealth offices, Barbara sent her private office staff round to the Fabian Society to collect every available copy of a pamphlet she had written on international development, and instructed them to treat it as a blueprint. Within a year, she had established her department and secured its budget, and demonstrated a flair for the photo-opportunity desperately needed by a government already wracked by internal tensions and an economy in crisis.
Wilson promoted her to the Department of Transport (even though she couldn't drive), where her dominant traits as a minister became clearer: she demanded total support from her civil servants - in a very public battle of wills, much effort was devoted to trying to move her permanent secretary, Sir Thomas Padmore; she had a good eye for what was both desirable and achievable, and the left's unshakeable belief in the power of government to plan from the centre.
In her 2 years at transport, she transformed the culture of motoring with the introduction of the breathalyser and the seatbelt. But with the economy still perilously fragile, despite the devaluation of 1966, Labour was locked in its long and, ultimately failed, attempt to control inflation while maintaining full employment. A pay policy was unavoidable, but equally unpopular.
Wilson wanted Barbara to bring her dynamism and popularity to selling the pay restraint to an increasingly nervous parliamentary party. He created a new department for her, Employment and Productivity. And she was brought in to the heart of government as first secretary, a title generously foregone by another political intimate, Richard Crossman. It was the pinnacle of her career, and, from it, she heroically flung herself, convinced of her own rightness, down into the deep gulley of union reform.
Convinced that a statutory pay policy was an instrument of socialism - a brake on the industrial might that won inflationary pay claims at the expense of the economy and of weaker unions - Barbara was brought up short by trade unions totally resistant to any restraint on free collective bargaining. Under pressure from the Tories, and wrapped in an unshakeable confidence in the duty of government to bring order to the chaotic state of British industrial relations, she attempted to deliver a socialist solution - "The trouble with Barbara is that she thinks anything she does is socialism," sniffed a contemporary. In Place Of Strife was the inflammatory title of a white paper that proved to be the most divisive attempt at legislation for 35 years.
Although there were many worthy proposals intended to strengthen trade unions, all anyone saw were plans for compulsory strike ballots and a cooling-off period, both to be underwritten by sanctions. Barbara, who believed that, given time she could make anyone love her, wanted a long, evangelical campaign to build up popular support. Roy Jenkins, the chancellor, was desperate for some reassuring morsel to feed the bankers hungrily circling the floundering pound. She was forced to accept a short bill to enact only the penal clauses.
In the face of a campaign illuminated by the startling duplicity of senior colleagues, including the then home secretary, James Callaghan, and an entirely hubristic challenge from the unions, pathfinding for the Thatcher assault on trade union rights 10 years later, Barbara and Wilson rashly made the legislation an issue of confidence. Egged on by an enthusiastic press (with the exception of the Guardian), Barbara took the battle to seaside resorts and spa towns around the country in a dramatic, and hugely popular appeal, to individual union conferences. In barrister's black, the taut passionate figure aroused the admiration of millions.
But trade unionists, led by Vic Feather at the TUC, found her ignorant, inflexible and hectoring. Friends on the left could not understand why she was doing the Tories' work for them. And Wilson's more ambitious enemies planned for what they were sure was his imminent downfall. There were genuine fears the party could be split into union-sponsored and independent MPs, another 1931.
The cabinet - and, ultimately, even the chancellor - deserted the bill. Wilson and Barbara were forced into a humiliating defeat, behind a fig leaf of "solemn and binding" agreements that the TUC and the unions would work together to try to restrain the unofficial strikes that were undermining economic recovery.
Barbara's stock crashed to earth. But the ramifications went far beyond personal disaster. The episode accelerated a renewed alienation between party activists and the Labour leadership. Local parties became vulnerable to infiltration by Trotskyite groups, like Militant, preaching the politics of betrayal.
The leadership of the left - never quite within Barbara's grasp - was now torn between Michael Foot and Tony Benn. The unions, after Edward Heath's failed attempt at union legislation, which was uncomfortably close to Barbara's own, agreed to the social contract, a promise of voluntary pay restraint in return for legislative favours from a future Labour government.
Back in power in 1974, Wilson loyally put Barbara - who had been thrown off the elected shadow cabinet in 1972 - into the Department of Health and Social Security. Here, in a period of government often overlooked, she launched a last effort to push back the frontiers of the welfare state. But although it was marked by notable achievements - like the introduction of Serps, the scheme for second pensions which was intended to transform the old age of millions of low-paid - she squandered her last political capital on an ideological battle over pay beds in the NHS.
This time, the backbenches and the unions cheered her on. But it was at a heavy cost to the health service: at one stage, all hospital doctors, from the most junior to the most senior, were involved in industrial action which closed accident and emergency wings, and tainted industrial relations for years afterwards.
Before she could bring in the legislation for which she had fought so hard, Wilson resigned. His successor, Jim Callaghan, sacked Barbara with unexpected brutality, and her pay-bed reforms ran slowly into the sand. By 1979, only a quarter of all pay-beds were phased out, while the private sector outside hospitals blossomed unrestrained.
There were other, more subtly achieved and lasting, successes. Although she always rejected single-issue politics as a distraction from socialism (like Mrs Thatcher, she was a politician who was also a woman - tough, flirtatious, vain, often hot-tempered, capable of tears in moments of drama - rather than a woman politician), and she brutally dismissed recent attempts to make Westminster a kinder, gentler place, her most enduring achievements came on behalf of women.
Equal pay was the most notable, slipped past a reluctant Roy Jenkins in a late-night bid in 1970 to avert a backbench revolt. She won other vital concessions for women in pensions reforms. She introduced child benefit, and insisted it went into the purse not the wallet.
Even when she gave up the Commons in 1979, she could not give up politics. After a lifetime's opposition to the European Union, she became the leader of the Labour group in the European parliament, where, for another 10 years, she harried commissioners on the common agriculture policy, before finally demanding a seat in the Lords in 1990 from the then Labour leader Neil Kinnock.
She remained an active and determined campaigner for pension rights - the chancellor, Gordon Brown, called her "my mentor and my tormentor" - and against animal cruelty until her final illness. Her passion for politics was given full rein in her final incarnation as national treasure. As the figurehead and part-inspiration for the 1990s campaign to restore the link between pensions and earnings (which she had introduced 20 years earlier), Barbara finally won the near-universal applause of which she had so long dreamed.
Committed to the socialism of her youth, she hated what she thought Tony Blair was doing to the party. But her loyalty to the Labour movement was unfaltering. Contemporaries, infuriated by her singleminded and relentless pursuit of her objectives in government, recalled, in the cosy glow of nostalgia, her huge appetite both for life and for the fight. She was a woman who delighted in dancing with the enemy at night, before spearing them with her invective the next day.
Barbara and Ted, who died in 1979, had no children, but were devoted to their nieces and great nieces and nephews.
Denis Healey writes: Barbara Castle was an iconic figure in the postwar politics of Britain, personally attractive to friend and foe alike. Many found her energy and intelligence irresistible. She had red hair like other Labour women - Ellen Wilkinson between the wars, and Patricia Hollis today. She was always concerned about her appearance, and even as a minister had her hair done every day.
Although we often disagreed on political issues, particularly when she was a member of the Tribune group, Barbara and I had a lot in common.
I was a boy of 11 at Bradford grammar school when she was a prefect at Bradford girls' grammar school. As MPs, both of us worked as journalists, because in those days we could not live on an MP's salary alone. We served together on the national executive of the Labour party, and for many years in Labour cabinets.
Her time as a civil servant during the war had given her experience invaluable for work as a minister. Yet she was one of the few leading politicians who kept an interest outside politics - particularly poetry and walking.
Both of us spent some years as members of the European parliament. I always regretted that I was abroad when she was defeated in cabinet on her proposals to strengthen control of the trade unions, though her white paper, In Place Of Strife, caused years of civil war inside the Labour party.
She told me she was glad I was a pugilist and not a patrician, and dedicated my copy of her autobiography, "Affectionately to Denis, the man I love to fight." When she once complained that I was crucifying her, I replied: "Your hands do invite the nails."
Barbara Anne Castle, Baroness Castle of Blackburn, politician, born October 6 1910; died May 3 2002
Face To Faith and the weekend birthdays have been held over