Before Tony Blair started filming for his hour of questioning on the G8 summit, to be screened around the world on MTV today, he had a photoshoot with Bob Geldof, his co-host for the programme. Bob nuzzled into Tony’s neck for the cameras, leaning his head comfortably on his mate’s shoulder, his long hair draping across the Prime Minister’s suit. This was Mr Blair’s rock’n’roll moment, an hour of setting-the-world-to-rights discussion with a studio audience of idealistic teenagers, in which he got in touch with his own inner idealistic teenager, and very much in touch with his own rock star, Geldof.

Things were to get more rock’n’roll later on, with statements of brotherly love between Bob and Tony normally seen only in drunken bandmembers, and a protracted period when filming had to be stopped for soundmen to rummage in Mr Blair’s trousers. Mr Blair, looking vaguely terrified as the men dealt with the Prime Ministerial rump, said: “This is the best thing that’s happened to me all day.”

But for now the pair could chat about whether their daughters were going to the Live 8 concert at the weekend, and when Geldof joked with a teenager sporting an Afro that he looked like a member of the Seventies band Boney M, Mr Blair said: “I was thinking that, but I didn’t say it.”

This was not the only way Geldof emboldened his friend. Mr Blair was in expansive mood, relaxed also because, although he faces a tough round of negotiations with leaders of the West, the title question of the programme was “Who or what is G8?”. This was a different world from the debate he conducted on MTV two years ago on Iraq. He could be the good guy or, rather, the rebel, standing up for what he believed in.

“Thirty years ago I was about the same age as people here,” he said. “Thirty years on I can do something about these issues, so I should.”

It was in this spirit that when MTV flashed a survey of its viewers on screen showing that 95 per cent of them thought that President Bush was not doing enough on climate change, Mr Blair laughed.

When Robin, from Hong Kong, one of the 49 teenagers in the audience drawn from 24 countries, asked: “Could President Bush just be wrong?”, Mr Blair joked sarcastically: “Now that’s a revolutionary thought!” But he then went on to voice his own radical thoughts, that the Kyoto agreement on climate change was “in the past” and that given America was not going to sign it, “let’s leave that to one side”.

“What I’m trying to do in the G8 is get an agreement that we need a new dialogue, not just for countries from the G8, but also countries such as China and India, for the future.” And he praised Geldof for not acting too much like a rock’n’roller. He said: “These guys have not behaved like rock stars, parading idealism.”

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