Prime ministers like to plan their legacy. For Tony Blair it was peace in the Middle East, for Gordon Brown an end to boom and bust.

Yet before James Purnell dropped his bombshell on Thursday night, it looked like Mr Brown might have earned his place in the history books by becoming the first prime minister to be dumped by e-mail. A group of Labour rebels are still aiming to gather enough cyber-signatures from MPs calling for him to step down – though their efforts may now have been overtaken by events.