Wales and Northern Ireland Secretary Peter Hain has launched his attempt to become Labour's deputy leader.
Peter Hain has held several posts in Tony Blair's government
Formally announcing his candidacy at the TUC conference in Brighton, he warned against a "big lurch" in the direction the government has taken.
The Neath MP said: "Any idea that we turn our backs on the prime minister and on Tony Blair's success as Labour leader is, I think, mistaken."
Last week he announced his support for Gordon Brown to succeed Mr Blair.
Mr Hain, aged 56, confirmed that he would like to take over as Labour's number two when John Prescott stands down.
Mr Prescott has said that he will go when Mr Blair leaves Downing Street.
Mr Hain said the party had to build on Mr Blair's success.
"What I think people want is not some big lurch away from the direction which we have taken as a government, because it has been the most successful government in living memory for Britain in terms of full employment and economic stability," he told the BBC.
"What we need to do is make a bridge to the future that builds on our success and doesn't turn our back on our success.
"Al Gore made that mistake in the US in turning his back on President Clinton's success and he lost."
Mr Hain said Labour needed to "rebuild, to renew and reinvigorate and reconstitute that progressive coalition which has been fragmented over recent times."
Mr Hain's candidacy for the deputy leader post marks the latest stage in a political journey which has taken him from president of the Young Liberals and anti-apartheid campaigner into the Labour cabinet.
He is expected to face competition from several other senior ministers also vying for the job.
John Prescott has said he will go when Tony Blair stands down
Mr Hain has been working for many months to gain backing from the unions. Their support will be crucial in any deputy leadership contest, as union members hold one-third of the votes.
Mr Hain was born in Nairobi and brought up in South Africa. He was educated at Pretoria Boys High School, the University of London and Sussex University.
He was a leading anti-apartheid campaigner and in 1969 made headlines with his disruption of the all-white South African rugby team's tour of the UK.
He left the Liberals to join Labour in 1977. He worked as a trade union official until entering the Commons at a 1991 by-election for the traditional south Wales valleys Labour stronghold of Neath.
His first job in government in 1997 was as a junior Welsh Office minister, where he was responsible for managing Alun Michael's campaign for the leadership of Welsh Labour. He also had junior ministerial jobs in the Foreign Office and Department of Trade and Industry.
In October 2002, he replaced Paul Murphy as secretary of state for Wales, and in May 2005 also took on the same job in Northern Ireland - coincidentally, again replacing Mr Murphy.
Meanwhile, a meeting of Welsh Labour MPs to discuss the party's leadership crisis has been called off following appeals from both Mr Blair and Mr Brown.
The Welsh group of the parliamentary party had planned to meet on 18 September, when MPs were expected to discuss issuing a statement calling for the prime minister's resignation.
Several MPs from Wales were prominent among those who called on Mr Blair to set out the timetable for his resignation. The issue is particularly relevant in Wales ahead of next May's assembly election.