they would have to take down the Cabinet, the Chiefs of the Defence Staff, the leader of the opposition, the heads of the Security services and the top legal bods in the Gov't,
Excepting Cameron, one assumes these people are old flatmates and cronies carefully appointed for their sympathy with Bliar. Their heads roll if Bliar goes so they are perhaps less likely to resign on principle.
If Cameron sneaks into a power vacuum in the centre ground then this country has no opposition. The managed society will be fully upon us with a choice of three centrist parties. If you disagree with a major issue you will have nowhere to go.