PRIME Minister Tony Blair described her as "a great heroine". He said: "Barbara Castle was one of the dominating figures of the Labour movement of the last 50 years, a radical independent spirit and an extraordinary pioneer for women in politics.

"Courageous, determined, tireless and principled, she was never afraid to speak her mind or stand up for her beliefs.

"She was loved throughout the Labour movement and recognised as an outstanding minister in the many high offices she held.

"Even when she left the Commons after a remarkable career, she went on to lead Labour in Europe and to be an effective contributor in the Lords. Right up to her death, she remained a formidable campaigner on behalf of pensioners.

"She leaves behind a legacy of achievement of which any politician would be proud.

"Britain has lost one of its great political figures and the Labour movement a great heroine."

Her successor as Labour MEP, Gary Titley, now representing the North West of England, said: "Barbara was a formidable fighter for the Labour cause.

"She was totally dedicated to improving the lives of ordinary people. Few have made a bigger impression on British history."

Baroness Boothroyd, the former Commons Speaker, who was once Barbara Castle's secretary, said: "Barbara never retired from active politics. Her death creates a vacuum on the political scene.

"She was an indomitable fighter for women's rights. In recent years she championed the cause of pensioners. Barbara could always be found campaigning for her deeply held socialist beliefs."

Former Labour leader Neil Kinnock and his wife Glenys said in a joint statement: "For Barbara, only the word unique will do. Her passion blazed and her courage held steady throughout her long life. She needed both because she was always happiest at the eye of political storms.

"Her friends loved her because of -- sometimes in spite of -- her bluntness and her boldness. She repaid that support with deep loyalty and great kindness."

Sir Bernard Ingham, who was Barbara Castle's chief information officer before he became Margaret Thatcher's press secretary, said: "She was an extremely courageous politician who as a left-winger recognised in the Department of Employment and Productivity in 1968 the difficulty of living and working with trade unions.

"She sought to complement their powers with responsibility with the White Paper In Place of Strife. She got no thanks and was treated badly by many in the Labour Movement. I have the greatest admiration for her and am very sorry she has died."

Tony Benn, who served alongside Lady Castle in government, said: "Barbara was a very very remarkable woman, a woman of powerful intellect and a powerful figure of the Left.

"She was a very successful minister for international development, she introduced the breathalyser.

"As Secretary of State for Social Services she linked pensions with earnings, which meant that every pensioner on retirement could look forward to his pension being up-rated with earnings.

"This was abolished by Margaret Thatcher and has not been introduced by this Government.

"She was also a diarist and so has left a record of her life behind her. She was a woman of extreme integrity and had a very very influential life."

Gordon Lishman, director general of Age Concern, said: "Barbara Castle was a remarkable woman who will never be forgotten for her vigorous campaigning for pensioners' rights. She was also a powerful champion for older people."

Former Labour prime minister Lord Callaghan, who is 90 and who clashed with Baroness Castle from time to time, said: "I am naturally sorry to hear of her death since we have been colleagues for 50 years or more.

"She was a superb politician and she deserved success for many of the causes she fought for through her sheer ability, tenacity and hard work.

"I was always sorry when I had to oppose her, but she was a fighter who never despaired when she lost and rejoiced when she won. She fought to the end."

Conservative leader Iain Duncan Smith said he was saddened at news of her death.

He added: "She was a hugely significant figure, with a sharp political brain, who led a very full life both in and out of politics.

"She was a tireless campaigner with a massive character. Even in her later years, watching her campaigning on pensions, one was reminded of the huge enthusiasm and determination she brought to everything she did."