Were I a Labour MP, I wouldn't, were I Tory or Lib, I would.
From Labour's point of view, given the fact that there must be a GE within only a year, what advantage would be gained from doing a Julius Caesar type assassination on the leader? I would say none because not only do they have no one with the political stature or clout to succeed him, but it's exactly what the opposition are desperately hoping for to assist their aspirations of forcing an early GE.
The Tories, although ultra vociferous in their calls for Brown to go, have yet to map out their plans for the country should Cameron become PM. He's all bluster and no substance. What exactly are their policies? Every PMQ's is littered by demands to Brown from Cameron "to go", yet I have yet to hear anything of substance from him.
And unless we get PR, you can forget the Libs, they've no chance under the first past the post system.
Labour are miles behind in the current polls and must be bracing themselves for disaster tomorrow in the local and European elections, but that's not what really matters, it's what happens when there is a GE. For Labour to change leaders now would be for them political suicide.