Andrew Grice: PM has backing of the Commons – but it won't last

The Labour leader has left himself room to criticise if things turn sour

What a difference a weekend makes. Last Friday, David Cameron was greeted as a hero in the Commons amid the euphoria and surprise over securing a UN resolution to act in Libya.

Yesterday's six-and-a-half hour Commons debate was a much more sober affair. If it looked briefly on Friday that Mr Cameron's first major foreign policy test could boost his standing with a Thatcher-style "Falklands factor", yesterday the dark shadow of Tony Blair's disastrous adventure in Iraq hung over the chamber.

The same MPs who queued up to heap praise on the Prime Minister three days earlier came armed with a long list of tricky questions. Could the military operation target Colonel Gaddafi? What was the end game? What if there is a stalemate in which Gaddafi clings on to power? What was our plan for a post-Gaddafi Libya (we didn't have one for Iraq)? And so on. Wisely, Mr Cameron did not pretend to know them all, admitting: "It is easier to start these things than finish them... There will always be unforeseen consequences".

For now, Mr Cameron has the overwhelming backing of the Commons. But he knows that could change. Yesterday Ed Miliband was supportive and statesmanlike. Yet the Labour leader has left himself room to criticise if things turn sour. He appears to have learnt from the Tories' gung-ho approach to the Iraq war, which prevented them getting any mileage when it resulted in disaster. Mr Cameron had his doubts then. He enjoys no such luxury now.