Prime minister Gordon Brown has backed away from a suggestion by Lord Mandelson that he would take part in a US-style, live television debate with David Cameron during the next election.

Prime minister Gordon Brown has backed away from a suggestion by Lord Mandelson that he would take part in a US-style, live television debate with David Cameron during the next election.

The business secretary, who is deputy prime minister in all but name, said yesterday that it was likely that Mr Brown would take on Mr Cameron in a pre-election bout. "I don't think Gordon would have a problem with that," he said.

"While Cameron is good with words, he doesn't have the ideas or policies to back them. I think people would see through the smile."

Lord Mandelson is convinced that Mr Brown's gravitas will shine over his rival's more lightweight style. "The more the public sees of them, the more they'd realise that Gordon is the man with the substance," he said.

He said a debate could expose Mr Cameron's weaknesses, claiming the Conservative leader "lacks substance" and "might come across as someone who exudes effortless superiority in public but loses his rag in private".

However, Downing Street immediately played down any suggestion that the prime minister had changed his line on refusing to give the opposition a chance to land a free hit during the crucial election period.

Mr Brown's political spokesman said: "The position hasn't changed. Voters have the chance to compare the party leaders each week at Prime Minister's Questions."

High-profile TV showdowns are a fixture in the US, where they are seen as having the potential to turn elections, but it would be a high-risk strategy for Mr Brown. He is regularly bested by Mr Cameron during their weekly encounters at Prime Minister's Questions when Mr Brown's ponderous mastery of statistics leaves him looking slow compared to the light-footed Tory leader.

Earlier this month Mr Cameron repeated that he was prepared to put himself forward for the debates, just as he had debated with David Davis on live TV during the 2005 Tory leadership contest. Compared to Mr Davis, the performance of the virtually unknown Mr Cameron was seen as crucial in securing the party leadership.

He said yesterday he would be "delighted" to have the chance to go head to head with the prime minister. "I have always supported television debates at election time between the leaders of the parties," he said.

"I have pressed Gordon about it before and he was totally against it. If he has changed his mind, I will be delighted. I think television debates will help engage the public, help to actually answer some of the questions at the heart of the election, and help bring the election alive in some way."

Lord Mandelson's apparent clanger came in one of a series of media interviews he has given in the parliamentary close season in which he has acknowledged that most people thought Labour would lose the election. He urged his party and MPs to fight as if they were rebel underdogs rather than the established government if they were to have a chance to win.

"Of course it's difficult, and of course we're coming from behind. We are the underdogs in politics now," he said.

"It's going to be harder for us to be insurgents rather than simply incumbents. It's going to be harder for us to convince people that we are going to continue to be the changemakers in British politics."

He added: "When the time comes not necessarily to be tested by these events but to be judged by the results of our policies, I think that you'll find that Gordon Brown and his government will be thoroughly vindicated."