Prime minister's questions sketch
By Nick Assinder
Political correspondent, BBC News website
Now there is even more reason to wonder exactly why six Labour MPs are battling to become deputy leader.
Mr Blair said it was the leader who mattered
They are already learning to live with the prospect that they will not be following in the heavy footsteps of John Prescott by being given the job as deputy prime minister.
Now, in that withering phrase that always precedes a slap down, the prime minister has told them "with respect" that the important thing is the leadership.
Of course, everyone already knows that under Tony Blair it most certainly was the leadership that mattered - to the point that he was regularly accused of running a presidential, one-man-band approach to government.
Gordon Brown, however, is signalling he wants to do things differently and in a more collegiate fashion and "listen".
Mr Cameron believes if he listens to the deputy leadership candidates he will lead Labour back to the days of union militancy, high taxes and probably plagues of locusts as well.
The contest, he declared, was a cross between Big Brother and the Muppet Show.
And he was doing his best to embarrass both the outgoing prime minister and the incoming one with suggestions that the New Labour project was being dismantled in front of their eyes.
Mr Cameron claimed contenders were the Muppet Show
Deputy leadership candidates were lurching to the left with plans to give the trade unions more money and more power, oppose the replacement of Trident and increase taxes, he said.
Did Mr Blair agree with them, he wanted to know.
Of course he doesn't - the real question is whether the candidates themselves really believe it all or are they just saying these things to appeal to the traditionally leftish union and grassroots voters.
Still, freed from any prime ministerial or leadership constraints, Mr Blair made it plain exactly what he thought of these remarks.
"No, I do not agree with these statements," he said before attempting to turn the focus onto Mr Cameron's lack of leadership over, for example, grammar schools.
Mr Blair was never the most assiduous when it came to answering questions, now he doesn't event attempt to disguise the fact and he spent his time ridiculing the Tory leader and his record.
Former Tory leader Michael Howard summed it up during a television interview later.
"The prime minister was not taking anything seriously, so we should not be taking anything he said seriously either," he said.
That might be some comfort to the six would-be deputies.