Tony Blair is still a "strong" prime minister despite new calls for him to quit early, Local Government Minister David Miliband has said.
Blair has said he had hoped to end speculation about his leaving date.
Mr Miliband said Mr Blair had already been candid over his departure plans.
He was speaking after MP Ashok Kumar, ministerial aide to Hilary Benn, wrote in an article that the prime minister should step aside "rapidly".
Mr Kumar told the Northern Echo it was time Mr Blair revealed his exit plans and suggested he should go before 2008.
Asked whether Mr Blair should come clean about when he would step down, Mr Miliband said he believed no prime minister "has been more candid" over his plans.
"I think we have got a very strong prime minister and an outstanding leader-in-waiting in Gordon Brown," he told BBC Radio 4's Today programme.
"I think that makes people like me, on the Labour side of politics, not just confident about the party's future but also about the country's future."
'Tell us the date'
Mr Kumar, the normally loyal parliamentary private secretary to international development secretary Hilary Benn, claimed the prime minister had been damaged by both the Iraq war and the allegations over secret loans.
He used his article to urge Mr Blair to step aside for a "smooth and rapid" succession to the Chancellor, Gordon Brown.
The Middlesbrough South and East Cleveland MP told BBC Newsnight it was time for Mr Blair to tell people when he planned to step down.
"If he has a date perhaps he could tell, sit down with Gordon Brown and both of them share that date together and tell the rest of us as well," he said.
"As long as there's an agreement between both of them and they can tell us the date I'll be as happy man so then I know when prime minister's term's going to come to an end and Gordon Brown's going to take over."
Mr Kumar added: "We can't go on to 2008 and 2009, as speculation has existed, but the date has got to be before that.
"But it's got to be between the two of them and if in the end the two of them think it's got to be 2008 or 2009, well OK so be it. My own opinion is it has to be before that but they have to agree."
After talks with Chief Whip Hilary Armstrong, Mr Kumar has issued a statement saying he was not being disloyal to Mr Blair or the government.
He has kept his post as a ministerial aide, although Mr Benn has distanced himself from the comments.