Blimey!

Did not see this one coming.

David Davis is to resign as shadow home secretary in a move that will shock Westminster and be a severe blow to Tory leader David Cameron. Mr Davis is also to stand down from his parliamentary seat in Hull and call a constituency by-election to highlight the issue of the erosion of civil liberties in Britain.

He will then stand as a Conservative candidate again for the same seat, in the by-election set to be held on July 10, while campaigning on the issue of civil liberties in the Hull area and throughout Britain.

I'm not sure I understand it either. The Tories were opposed to this legislation in the first place, it will now almost certainly be defeated in the Lords, and it will then move back to the Commons where the Tories will oppose it again. The reason might be that Davis said, when asked, that the Tories would repeal this when they get into power. If that pledge is to be repudiated, that would explain his resignation as a matter of principle. Otherwise this move looks very odd indeed. Sure to be more later...

UPDATE: The Coffee Housers seem to agree:

A Tory source has just explained to me what Davis is up to. He wants to stand down, force a by-election, then run a campaign on 42 days and declare that ‘the people have spoken’. Why? Well, one reason being put about is that he wants leverage in the internal debate over whether or not the Tories should commit to repeal 42 days.
This is high-risk stuff. Then again, Davis is not averse to risk - as the Alan Clarke diaries show.

UPDATE: Nick Clegg has said that the Liberal Democrats won't contest the bye-election. I suppose the clever move would be for Labour to do the same, saying that it's a frivolous waste of public money... Can't quite see them doing this though.