Cameron’s just finished giving his announcement to the media, and his strategy is clear: A direct invitation to form a coalition with the Liberal Democrats, ticking all the ’4 policies’: Pupil premium, scrapping ID cards, committee to consider electoral reform and “tax fairness”. The red lines are immigration, Europe and Defence. It’s everything that Clegg said he would look for in seeking to form any kind of deal, and it’s something right wing Tories will find difficult to refuse.

The deal might not actually be any good for the Lib Dems – it’s NOT a referendum on PR. It’s NOT a commitment to raise the tax threshold, but Cameron’s done it in such a way that it’ll be extremely difficult to turn down without looking churlish and selfish.

Lib Dems will never adequately be able to explain why they’ve turned it down. If PR really is the only thing that matters to Clegg and the Lib Dems (and it’s starting to look, disgustingly, like it is) and they go instead with a ‘nothing *but* a referendum’ deal with Labour (and, with it, a referendum on Scottish Independence to get the Nats involved too) then they’re going to look like a right bunch of twats.

Not only that, the only question anyone will ever ask Nick Clegg again is this: “If PR was the precondition of Lib Dem support, why didn’t you say this before the election? What happened to the 4 priorities?” and no amount of waffle or explanation will make this go away. Cameron is holding Clegg at his word – and taking a huge risk with his own party at the same time.

Will the Lib Dem MPs let this happen? Waiting patiently for Clegg’s reaction…