In Haltemprice & Howden, the Tories are vulnerable to a LibDem swing. The Liberals would require less than a 6% swing to take their seat and their candidate David Nolan has experience of three previous General Elections.

The sizeable Labour minority in the constituency would have to calculate what would best upset Cameron's ascendancy in the polls. Voting LibDem or for an Independent David Davis - or sticking with Labour and leaving a factionalised Tory Party to rip themselves up.

David Cameron's most sensible strategy would be to back David Davis' re-election - even as an Independent. Davis would be pressurised to take the Tory whip before long - yet would be on the backbenches for the next decade. Cameron could this way tar Davis as a primadonna without causing a split in the local party that could reverberate nationally.

Or he might have another old mate from Eton who fancies the seat.

Labour has an interesting strategic opportunity in this by-election. While I must clarify I absolutely abhor this 42-day detention measure, I can't deny it is a Labour policy. If Labour selects a candidate who is pro-42 days, we would be the only party contesting the by-election in H&H on that platform (presuming the DUP doesn't stand). In essence, we could take Davis up on his offer of turning the by-election into a referendum on 42-days. While that could upset our core vote, we could very well achieve a direct swing from the Tories on the issue and achieve a respectable increase in our share of the vote.