The Sketch: Once Mr Blair has chosen to believe something, evidence is redundant

The incident is reported like this. Tony Blair meets one of our foremost novelists at a Britart reception. "Love your paintings," he says. "Er... I'm a novelist," the novelist says. Our leader's composure is undisturbed. "No, but you paint as well, I've got a couple in my house. They're great." The Prime Minister moves on, the novelist is left with interesting evidence about the pathology of power. Once Mr Blair has chosen to believe something, evidence is redundant.

The incident is reported like this. Tony Blair meets one of our foremost novelists at a Britart reception. "Love your paintings," he says. "Er... I'm a novelist," the novelist says. Our leader's composure is undisturbed. "No, but you paint as well, I've got a couple in my house. They're great." The Prime Minister moves on, the novelist is left with interesting evidence about the pathology of power. Once Mr Blair has chosen to believe something, evidence is redundant.

Do you believe the novelist (who makes things up for a living)? Or the Prime Minister (man of honour)? If you believe the novelist, you will have to believe our Prime Minister will say anything to win an argument. Well, shame on you! Stop dragging me down to your level!

Usually it doesn't matter enormously what the Prime Minister chooses to believe. Will the new generation of council tenants be able to buy their new, Johnny-built, £60,000 council houses? Yes (John Prescott on Tuesday); No (Tony Blair on Wednesday). Maybe tenants will be allowed to buy their shack but not sell it; that would be the circle-squaring solution. But whatever the ins and outs of it, the only people affected will be the poor devils who have to live in them.

But is the Prime Minister going to help bomb Iran? It's a question that matters a bit more generally. Michael Meacher, noting reports that America was considering bombing Iran's nuclear facilities and US special forces were already in the area, asked the Prime Minister to give an unequivocal and categoric assurance that he wouldn't support such a raid by America or its proxy, Israel.

Mr Blair would not give such an assurance. Not aggressively, you understand, he just glided past it, saying: "I know of no such contemplation by America." It's the second time he's said this. "I haven't heard any talk about that," he told the House last time.

Cynics will say his intelligence briefings must have hit new lows for this to be true. MI6 must have cancelled its subscription to The New York Times. Others will point out that "contemplation" has more than one meaning, and "by America" could mean anything. As for the "I" in "I know" we would have to examine the hierarchy of selves that are capable of knowledge before coming to any kind of conclusion. Maybe Mr Blair has chosen to believe it, in which case argument is redundant.

At times no one on the front bench was listening to their leader at all. Among the dozing, dreaming and note-taking, Jack Straw and Gordon Brown continued their ostentatiously chattering relationship. Mr Straw has just come back from Washington where he was giving unequivocal assurances that Britain wouldn't support a strike on Iran. Who cleared this sudden burst of independent action from our Foreign Secretary? Mr Blair? Possibly. Mr Brown? Surely.

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