Back in the 1970s, as a leading light in the anti-Apartheid movement and the Young Liberals, he was known as "Hain the Pain". His outspoken, unapologetic brand of direct action radicalism did not exactly endear him to the English establishment.

But Peter Hain's political talents were never in doubt and, once he switched allegiances to Labour in 1977, his long climb up the greasy pole always seemed to have an air of inevitability about it.

Mr Hain, 57, announced his resignation from the Cabinet today, vowing to clear his name over accusations that he acted illegally in failing to declare more than £100,000 of donations during his recent campaign for the party's deputy leadership.

It is far from being the first battle of his career, nor indeed his first brush with the law. Born in Nairobi in 1970 and brought up in South Africa to white parents who abhorred white minority rule, he recalled being woken up at the age of 10 by Special Branch officers searching through his bedroom drawers at the family home in Pretoria.

After moving to Britain as a teenager, Mr Hain continued his anti-Apartheid campaigning and was fined £200 for criminal damage in 1969 after leading a sit-down to disrupt a Davis Cup tie against South Africa in Bristol.

He also led the campaign to disrupt the 1970 Springboks rugby tour and helped bring an end to South African cricket tours, earning himself the soubriquet, from the Daily Telegraph, of Public Enemy No 1.

In 1972, he was sent a letter bomb, but it failed to explode because of faulty wiring. Three years later he was accused of a bank robbery, but acquitted after a ten-day trial. He is certain this was an attempt by the South African secret service to frame him, using a phoney lookalike.

In 1977, frustrated by the constraints of the Young Liberals, Mr Hain defected to Labour at the behest of Neil Kinnock. In the 1980s, as a member of the so-called “soft left”, he worked closely with Mr Kinnock, by then the Labour leader, on party modernisation.

That same year he was also a founding member of the Anti-Nazi League, which led the country's most successful campaign against racism.

He unsuccessfully fought Putney in 1983 and 1987, but became MP for the rock-solid Labour seat of Neath in a by-election in 1991. Soon after that, he became chairman of the left-leaning Tribune group.

When Labour stormed to power in 1997, Mr Hain became a whip and then a junior minister in the Welsh Office. His modernising skills and the effort he put into the referendum campaigns for devolution in Scotland and Wales had impressed Tony Blair and he joined the Foreign Office where he became Minister for Africa and later Minister for Europe.

Mr Hain had held a seat in the Cabinet since 2002 when he was appointed the Secretary of State for Wales. Since then he has held the positions of Leader of the House of Commons and Lord Keeper of the Privy Seal, Secretary of State for Northern Ireland and, until today, Secretary of State for Work and Pensions.

Despite becoming part of the establishment, his rebellious side stayed with him. In the New Statesman in 1999 he launched a scathing attack on his own Government by accusing it of ignoring the party’s traditional supporters. In 2003, as Mr Blair fought off calls for a referendum on the EU constitution, he suggested voters could use a European parliamentary election as a kind of back-door referendum.

Mr Hain was quickly slapped down, but his career was not derailed and he appeared to retain his unofficial licence as the permatanned critic of new Labour excesses.

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