John Reid has sparked speculation about a Labour leadership bid with a keynote speech on his party's future.
John Reid speaking at a Labour Party rally in south London
The home secretary said New Labour must continue after Tony Blair if the party is to win a fourth term in power.
He also backed Gordon Brown's record as chancellor but stopped short of endorsing him as the next leader.
Mr Reid's aides insisted he was simply talking about future Labour policy but Brownite MP George Mudie said it was a "marker" for a leadership bid.
The speech follows newspaper speculation Mr Brown would govern in a different style to Mr Blair if he became leader.
Speaking to party members in south London, Mr Reid said Labour should remain "New Labour" if it is to win a fourth general election.
He said it should continue to adapt itself to the aspirations of the majority of working people, even if they now aspired to different things than Labour had been promoting in 1997.
He said the Tories would try to "sow the seeds" of the idea that New Labour would end when Mr Blair stood down.
But he insisted New Labour's values were shared by every member of the Cabinet.
And he mounted a defence of Gordon Brown, who he said had been the victim of "personal attacks" by the Conservatives.
He said Mr Brown "towers above anything anyone in the Tory Party has ever aspired to or could ever aspire to".
But he also said Mr Blair's departure would raise doubts in voters' minds, especially as Conservative leader David Cameron was, in Mr Reid's words, "doing well" in presentational terms.
"With the departure of Tony Blair, people will start asking again whether Labour will stay New Labour.
"And with the arrival of David Cameron, they will no doubt ask, can Labour still win as the party best suited to govern?"
'Decades of work'
He said the answer to both "connected" questions was yes.
"If we remain true to the New Labour approach then we can, we should, and I believe we will secure and deserve another, fourth term in government."
He went on: "The Tories will try to argue that Tony Blair equals New Labour. They will say that when Tony Blair goes New Labour goes with him. That is not the case and we must show that it is not true."
Mr Reid suggested that rather than being the product of one person - Mr Blair - the New Labour concept is the product of decades of work.
Siobhan McDonagh, Mr Reid's parliamentary private secretary, said the home secretary "has never expressed a desire to be leader of the Labour party or prime minister to me".
But Brownite former minister Mr Mudie said: "I think the timing is important.
"I think it's an early attempt to put a marker down to get some of the Gordon Brown supporters to say 'we need a change of direction' so that he can say 'this is disloyalty to the leader and, therefore, I shall throw my hat into the ring or we shall find someone to do so'."
He told BBC Radio 4's World at One the speech was "probably the start of them finding a candidate to take on Gordon Brown".