Chris Kelly standing down is as significant as Douglas Carswell defecting

Defections from one political party to another don’t happen very often, and they make great political theatre, so they are rightly big news.

But in the week when Douglas Carswell switched from Tory to UKIP and made the blow doubly hard by doing the honourable thing and calling a by-election to get a public mandate for his decision, the media are wrong to have overlooked another, potentially even more significant announcement by a Tory MP, the obscure Chris Kelly.

Carswell’s decision may prove to be vital for the battle between the Tories and UKIP to represent Britain’s sizeable Eurosceptic right wing constituency. I happen to think it may herald a UKIP breakthrough into the House of Commons, which could see them with 6-10 MPs from Kent, Essex and Lincolnshire. 

But that represents a sideshow in a multi-way fight General Election, of similar significance to Labour’s fight with the Lib Dems. This is just about basic maths. The large number of votes changing hands in these two fights (Lab vs LD and Con vs UKIP) are definitely not to be sniffed at. Each vote lost by the Tories to UKIP in a Lab vs Con seat makes it more difficult for the Tories to win and easier for Labour to win. Each Lib Dem vote lost to Labour in a Lab vs Con seat has the same effect. There are a tiny number of seats which might even flip from Con to UKIP (as I have suggested, up to ten) or LD to Labour (about a dozen) – when either of these happens it put the Tories further from the winning line of an overall majority and Labour nearer to one.

But the big fight remains Lab vs Con because there are far more Lab vs Con marginals than any other type and only these two parties have any chance of forming an overall majority. 

And whereas the switches outlined above remove one vote or one seat from the Tories or add one vote or one seat to Labour, direct switches from Con to Lab, voters or seats, have a double effect. They reduce the Tory score AND increase the Labour score. Each voter switching like this reduces the Tory majority in a seat where Labour is second by two, not by one in the way the Con to UKIP or LD to Lab switchers do. Each seat that changes hands direct from Con to Lab also reduces the Tory lead in the Commons over Labour by two, not the one that Carswell winning Clacton for UKIP or Labour picking up a Lib Dem seat does.

And in any close marginal seat, studies of recent elections have shown having an incumbent MP helps you hold the seat because of their name profile, casework for people, and ability to communicate with voters. Incumbents get a particular bonus at the end of their first term because the new effect of their incumbency is added to the removal of the incumbency effect the rivals they ousted in 2010 had. So you would expect the Tories to do better than their average national performance at holding seats they gained in 2010, just as Labour MPs first elected in 1997 generally did very well when they first defended their seats in 2001. Mike Smithson’s analysis of the electoral impact of incumbency is here.

This is where the obscure Chris Kelly MP comes in. Mr Kelly is Tory MP for Dudley South one of the very marginal seats that determines the outcome of General Elections – it is number 75 on Labour’s target list. He gained it in 2010 and has presumably been working hard to build up an incumbency effect. And then on Monday he announced he is standing down at the General Election.

So the Tories will find it far harder to hold Dudley South than they would have done.

And because Dudley South is a Con vs Lab marginal it is twice as significant to the relative chances of both main parties forming a majority than Clacton is, whatever the defection and by-election brouhaha. 

Mr Kelly is not old and worn out by the cares of high office. He is only 36 and now loses a £50 bet he placed as a student in the 1990s that he would be PM by 2038.

Whoever his successor is as Tory candidate will have just a few months to campaign and build up a profile, such is the lateness of the decision. Labour candidate Natasha Millward has already been campaigning as candidate since July 2013.

Mr Kelly is a fervent Eurosceptic. He hasn’t defected to UKIP but by walking away from a marginal seat at almost the last minute he has certainly knifed David Cameron just as effectively as but with far less public attention than Douglas Carswell did.

And he isn’t the only 2010 intake Tory MP retiring after just one term. There are eight 2010 intake Tories already retiring, including the winners of seats gained from Labour such as Cannock Chase, Cardiff North, Erewash, Hove, North Warwickshire, South Ribble and South Thanet. In a party that is weak at picking women candidates compared to Labour, three of these eight are women. In contrast, not a single first term Labour MP is retiring.

Something is very badly wrong with the morale of the Tory parliamentary party. People who have dedicated their lives to becoming Tory MPs are bailing out after only one term. And it is going to have a big impact on a close General Election.