Grab a chair...

The impending departure of James Arbuthnot from the chair of the Commons Defence Select Committee signals the first by-election* for one of these posts since the system of elected chairs was introduced; and it should be an interesting one.

It's a plum job, commanding considerable prestige and, potentially, enormous influence.

With all kinds of uncomfortable cuts being made, the government desperately needs the aproval of the select committee, and Mr Arbuthnot has used that power wisely, and sparingly, maintaining a unified committee even when the party political flack was flying.

A successor with the same subtlety would be a major player in defence issues; someone less adept could fritter that influence away.

The post is reserved for a Conservative MP, under the share-out of chairs at the start of the parliament, but all MPs get a vote.

Initial soundings suggest that at least three of the four remaining Conservatives on the committee are at least eying the possibility of running - that's Col Bob Stewart, James Gray and Julian Brazier.

The name of the former minister Crispin Blunt is also being mentioned, and then there's Douglas Carswell, who ran for the post in 2010 on a promise to shake up defence procurement and buy more military equipment off the shelf rather than from big contractors like BAE.

He uses the formula made famous by Michael Heseltine when asked about the Tory leadership, saying he can imagine no circumstances in which he would seek election… but he thinks the next chair should do to them what the Treasury Committee chair, Andrew Tyrie, has done to the bankers.

There are vague murmurs about more ex-ministers and senior figures from other committees testing the water too.

One new entrant to the lists is the former Public Accounts Committee Chair, and current chairman of the Conservative backbench committee on Defence and Foreign Affairs, Edward Leigh, who will run on the basis of his record as an objective, collegiate chair.

All of which suggests there will be plenty of fun to be had… by Labour MPs.

With the sky dark with Tory hats being thrown into the ring, it looks as if the ultimate winner of the election will be decided by non-Tory votes.

Which means Labour votes.

This makes committee members nervous; they would prefer an insider who would be a continuation of Mr Arbuthnot by other means.

And they would be nervous about a chair who won as either a Tory loyalist, or, more probably, as a rebel who would set out to make trouble.

Either would be destabilising to a committee that depends on marshalling a non-partisan consensus.

And it will be an interesting appetiser for the next full round of select committee elections which will take place after the next general election, which I expect to be much more competitive than the last ones, as dozens of MPs vie to become the next Keith Vaz.

* There was a by-election for chair of the Procedure Committee a while ago, but this is the first departmental select committee, and there was also a mid-term election for chair of the Backbench Business Committee, in which the incumbent, Natascha Engel, was unopposed. I don't think that counts.