"He could ... remove Gordon Brown by deploying a nuclear resignation. Not his own, of course, because the Heseltinian doctrine about crowns and assassins holds good. But he has all the codes, and having persuaded David Miliband not to quit in May, he could easily unpersuade him in October. Assuming the polls remain hideous, and that a wretched party conference provokes a fresh eruption of despair, the hapless Foreign Secretary might leave the Cabinet 'in the interests of the party'. The tears welling up, Mandelson would tell Gordon that he can do no more to save him, and he'd be gone within hours. Ms Armstrong, one of the Blairite cabal of whom Mandy is undisputed leader, could then give up her seat. His lordship could renounce his lordship, be back in the Commons within the month, and Prime Minister by Christmas."
Sure, there are lots of improbables and imponderables in there: this is pretty much the Twilight Zone of political speculation. But you can't help but wonder whether the current PM will come to regret allowing Lord PM so much influence.