Thesis, from Jim Henley:
Thus an imperative to bomb Iran even - especially! - if all the options are bad and even potentially counterproductive and we can’t credibly threaten a land invasion and the notion of occupying the place brings laughter ranging in timbre from bitter to gleeful. Just as the Bush Administration and its more straightforward freelance publicists in the hawkosphere said we needed to topple Saddam Hussein to show that we could, the same crowd may feel that we need to bomb Iran for the same reason. So they superheat a problem (for the prospect of a nuclear-armed Iran is that) into a crisis (which it is not). The real reason to bomb Iran is to show that, even if our land forces are tied down, we can still mess you up.
Confirmation, from the Independent:
Differences opened up yesterday between Mr Blair and the Foreign Secretary over growing alarm in the US at the refusal of Mr Bush to rule out military action. Mr Straw said on BBC Radio 4 that it was "inconceivable" that Britain would support a military strike against Tehran. Four hours later, Mr Blair refused to go that far when challenged to do so at Prime Minister's questions by the former minister, Michael Meacher.
Mr Blair accused Iran of fostering international terrorism, and said young people were signing up to be suicide bombers directed at US and UK targets. " I do not think this is the time to send a message of weakness," he said.
British variant: few over here will actually come out and support a first strike on Iran. They'll just accuse people who actively oppose it of not taking the problem seriously. If it takes place, they'll say it had to happen because people who opposed it didn't take the problem seriously.