But the prime minister's spokesman suggested that the chancellor had refused to be drawn on the subject because he was determined that the BBC interview should be focused on the health service.

What Tony Blair and I have talked about is very private

Gordon Brown Chancellor

The spokesman said talk of a deal was "not on anyone's radar or agenda".

Mr Brown had said: "He's doing an excellent job. He will stay as prime minister and that's the right thing to do.

"But what Tony Blair and I have talked about is something very private."

Stunned

Mr Brown's answer clearly stunned veteran broadcaster David Frost, who told the chancellor: "I was gobsmacked because you didn't go one way or the other on that."

Brown and Blair: worked together for 18 years

And he added: "It's private, but it's going to intrigue people that you didn't answer the question."

Mr Brown said he and Tony Blair had a "very strong working relationship" which had been fostered over 18 years.

"When I'm talking to Tony Blair, we can laugh about people asking about us.

"I've known Tony Blair for 18 years and probably talked to him every day for 18 years, sometimes three or four times a day, about things that matter.

"It's a very strong working relationship and has been over that period of time."

'No agreement'

In an interview last May in London's Evening Standard, Mr Blair flatly denied that any leadership pact existed between him and Mr Brown.

"As Gordon and I both say whenever we are asked about this, there is no gentleman's agreement," he said.

You have two people that aren't working together

Mo Mowlam Former NI Secretary

Speculation has grown over the past few weeks about a rift between the two men.

On Saturday, Labour party chairman Charles Clarke appeared to contradict Mr Brown's economic tests for Britain to join the single currency.

This was interpreted by Liberal Democrat Treasury spokesman Edward Davey as the work of Blair's "stirrer in chief".

'Battle'

Two weeks ago, former Northern Ireland secretary Mo Mowlam said that rivalry between the prime minister and Mr Brown was "crippling" the government.

She told the BBC programme Cabinet Confidential: "When you have two people that aren't working together... it doesn't lead to positive, easy, decision making.

"You know there's a battle going on and people support, or people go to, one side or the other.

"I think that is just crippling for government."

In response, Chancellor Gordon Brown was lavished with praise by Downing Street, and Tony Blair's official spokesman hailed the chancellor as one of the finest finance ministers in the world with a fine track record of achievement.