By Ollie Stone-Lee
Political reporter, BBC News, Labour conference in Manchester
Ex-minister Peter Mandelson has warned union bosses not to think they can use the Labour leadership contest to win back their old power in the party.
Mr Mandelson says Tony Blair must not be forced out
The European commissioner told the Progress rally some union leaders felt "shut out" - but the party had changed.
Mr Mandelson said "old style operators" should not decide when and how Tony Blair steps down as prime minister.
He said rejecting the New Labour agenda would make the party look insincere in everything it had done in office.
Mr Mandelson said he was hopeful about Labour's prospects for the future but said the party had suffered a "moment of madness" in the recent leadership wrangling.
The way the succession was handled must be able to command voters' respect.
"I believe that we should recognise Tony Blair's exceptional talent and his achievements and what he has done for our party and our country," said Mr Mandelson.
"Let's celebrate the fact that at his tender age he has a lot more to offer...
"When he finally calls time, as he will, let it be his decision, let it be his timing, let it be his judgement when to name the day in the calendar, not the decision of old style operators in the party who thrive in smoke-filled rooms and are best left there, frankly."
Mr Mandelson, a close Blair ally, said the trade unions were the "ballast" of the Labour Party and their contribution should be welcomed.
But he said some union general secretaries and presidents would see the coming of a leadership election - where the unions have a third of the votes - as an opportunity to regain their former role in the party.
"They feel they have been shut out of the party but that was their choice to reject New Labour," he said.
Constituency parties had now found a voice and one-member-one-vote was here to stay, he said.
Mr Mandelson urged Labour activists to be proud of the government's achievements as that was the only way to persuade voters to recognise the successes.
"To reject New Labour now would be a rejection of the very sincerity and success of all our actions since we came to office in 1997," he said.
He said there needed to be a renewal of Labour's agenda.
But he said: "The new policy agenda needed for the next election will not come out of thin air or, by definition, it won't come out of one person's head."
Instead, all the talents of the party must be used in an inclusive way.
Mr Mandelson cautioned against returning to the "intolerance" of the 1980s where those putting forward alternative views had been dismissed as "mavericks".
Former Health Secretary Alan Milburn, seen as a possible future leadership candidate, told the meeting the party must not "abandon New Labour, we need to entrench and deepen it".
And Transport Secretary Douglas Alexander said Labour must not focus on the Conservatives and changes in the opinion poll ratings.
He said the party must concentrate on the way the world was changing and forge policies to meet those new challenges.