Melanie Phillips hits the nail on the head:

Yet that still doesn’t explain the exit frenzy gripping the party just over a year after Blair led it to a historic third election victory. Such a triumph has been vitiated by the real poison in British politics, the war in Iraq and Blair’s support for American foreign policy, President Bush and Israel. This is what’s really driving the comrades demented. It’s impossible to exaggerate the climate of virulent anti-Americanism and hatred of Israel which, extending way beyond the left into the centrist heartlands of Middle Britain, has so distorted British politics — and indeed, all but destroyed British rationality.

...The crucial question at this point in world history is whether the British government post-Blair will be as staunchly Atlanticist as he has been. The Tories have become alarmingly flaky in this regard, although a fight to resolve this within the party has yet to take place. Gordon Brown is known to have stars and stripes in his eyes, although ominously he has also let it be known that he would ditch support for certain aspects of US policy. For all his faults, Blair has displayed astounding courage and clear-mindedness in never wavering from his support for American foreign policy, despite the fury this has engendered among the voters and the consequent damage this has done to his whole political career. The key issue now in British politics is whether his successor — whoever it will be — will do the same.