Barbara Castle, who died on May 3rd 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 in Britain has yet produced, a unique witness to, and participant in, the 20th-century history of the left.
From the prewar unity campaign against Fascism 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.
Throughout her political career, she maintained a hard-headed pragmatism. 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.
Barbara Anne Betts grew up in the secure environment of a family with a need for belief. Her mother Annie, was a Labour councillor; her father, Frank, a tax inspector.
She toiled through Bradford girls' grammar school, and then at 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.
Soon after Oxford, she 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. But although she knew of the affair, Mellor could never bring himself to leave his wife. He died in 1942.
Barbara Castle 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.
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 Barbara Castle 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.
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 - and gave her the opportunity to reinvent herself, at the age of 53, as one of the most effective Cabinet ministers of her generation.
Wilson wanted her to bring her dynamism and popularity to selling pay restraint to an increasingly nervous parliamentary party. He created a new department for her, Employment and Productivity. 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 she 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.
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 Castle, 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.
The Cabinet - and, ultimately, even the chancellor - deserted it. Her 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.
Back in power in 1974, Wilson loyally put Barbara Castle - 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 she squandered her last political capital on an ideological battle over pay beds in the NHS.
Before she could bring in the legislation for which she had fought so hard, Wilson resigned. His successor, Jim Callaghan, sacked her 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.
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.
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 Castle was predeceased by her husband in 1979; they had no children.
Barbara Anne Castle, Baroness Castle of Blackburn: born 1910; died, May 2002