Wyler, all you say is true, but we march to the beat of US foreign policy. Gordon Brown is an Atlanticist, he will surely be keen to call the "business as usual" tune to placate Blairites. I am not as optimistic as you.
Do not forget that Cameron, Hague, Fox and the rest of the Tory inner shadow cabinet are even more pro Iraq War. They could shore up a Parliamentary vote. Remember how the Tories voted last time.