As social security minister, Mr Denham was responsible for steering through the government's recent pensions review, dubbed Labour's most important project by some.

The 45-year-old MP for Southampton Itchen will now be in the frontline for the setting-up of Primary Care Groups in April.

Many concerns have been expressed about the groups, which will see GPs, nurses and other health workers being responsible for commissioning care.

These include fears that doctors will bear the brunt of anger over rationing of care and will be overburdened by bureaucracy.

Frank Field

Mr Denham is used to political flak. He took over from the controversial social security minister Frank Field following a Cabinet reshuffle in July.

Before that, he was a junior minister in the Department of Social Security, responsible for fraud, pensions, national insurance and long-term care.

Alan Milburn moves up to the Treasury

He had been opposition spokesman on social security from 1995 to 1997 before Labour came to power.

Mr Denham, who has been an MP since 1992 after two unsuccessful attempts in the 1980s, has a comfortable majority of over 14,000.

At the general election in 1997, there was a 12.3% swing from Conservative to Labour in his Southampton constituency.

Environment

He has a background in the voluntary sector and has worked for Friends of the Earth, the British Youth Council and War on Want.

His environmental knowledge came in handy when he served on the Environment Select Committee.

Mr Denham honed his political skills in local government. He was a councillor at Hampshire County Council from 1981 to 1989 and then Southampton City Council until 1992.

There he chaired the housing committee and helped to expose a scandal over computer purchases at Wessex Health Authority.

Educated at Woodroffe Comprehensive School, Mr Denham was a leftish president of Southampton University Students Union and was involved in anti-nuclear protests, but has since moved rightwards.