The date of the General Election is:

May 6th. You read it here first.

How do we know? A contact whose property is used for General and Local election counts tells me he has received a letter from Whitehall asking him to refuse bookings for May 6th and May 7th and to re-arrange anything he has booked.

So May 6th - a Thursday (thanks Clothilde Simon) - is the one then.

18.24 Update: oh poo. According to a Labour Twitter thing when I posted this excitedly on Twitter, it's just a local election date. Does this mean I've got it wrong...