If the Lib Dems go into coalition with the Tories, they will get a referendum on the alternative vote system. That much, I think, they can be sure of. Labour, of course, seem to be luring them in with the promise that AV can be brought in without putting it to the people, and that full-blown PR can be looked at a little further down the line. But is that promise realistic?

I doubt it. Firstly, there are a lot of Labour backbenchers who won’t vote for AV or PR, and who favour first-past-the-post as much as the Tories do. And you can be sure that Cameron’s 307 MPs will do their best to vote down electoral reform if the Lib Dems throw the offer of a referendum in their face.

Moreover, an electoral reform act would take time (a year, maybe two) to get through both houses of parliament. And there is no way a Lib-Lab government would last that long. Long before AV could get Royal Assent, there would be another general election in which both Labour and the Liberal Democrats could expect to be punished for the way they had grabbed hold of power. As John Reid, the former home secretary, said last night, this coalition would mean deep unpopularity in England and, come polling day, mutually assured destruction.

Compare that with a deal with the Tories. OK, the tribal activists won’t like it (on either side). But the deal guarantees the Lib Dems that they will be able to implement at least part of their agenda (raising the personal allowance, introducing a pupil premium, political reform) while also giving them the opportunity to show the country that they are a serious political force, capable of governing in the national interest, and not just a none-of-the-above protest vote.

And then there’s a point I’ve made before: the real dividing line in politics is not the tribal one between left and right, but the intellectual one between localizers and centralizers, between market liberals and statist authoritarians. This is the ground around which the Conservatives and Liberal Democrats could rally, and do a great deal of good in the process. They just need to put their baser instincts aside first. Signs are that the Tories are prepared to do that. Will the Lib Dems follow suit?