Corby is a not just a by-election Labour ought to win: it is one it cannot afford to lose

The average reaction of most Labourites to last Monday’s news from Corby must surely have been: we never really took to you as an MP, but hey, thank you so much, Louise Mensch. To have pulled out of her marginal seat after only two years in the job, forcing an unwanted by-election in the middle of Cameron’s worst political period since becoming Prime Minister is to present Labour with a golden opportunity. This is not a statement of complacency: it is unarguable.

First, Labour is up in the polls and the Coalition has been in a terrible mess for months. And Cameron, in his current position, is damned if he does and damned if he doesn’t: if he bows to the current resurgence of the right in his party and fights Corby as a traditional Tory, he could lose those centrist voters he needs. If he fights as a Coalition centrist, he could get hammered by a UKIP protest vote, providing soul food for his critics on the right.

Second, whilst not sharing the visceral dislike of Mensch of some of my colleagues – in a non-partisan sense, perhaps MPs with an “interesting” CV are no bad thing for Parliament – one can see the electors of Corby are unlikely to thank someone for pulling out after such a short time in the job. And, admirable though her desire is to spend more time with her young family – heaven alone knows why anyone with a young family would want to do the job in the first place – it’s not like she didn’t know that when she signed up.

In any event, it is difficult to imagine being dealt a better hand to win a seat from the Tories than having it vacated by someone who, to locals, will inevitably be seen as a short-lived dilettante.

The trouble is, it’s such a good hand that it’s a double-edged sword. The pressure is now on Labour to perform: the Tories have already given the seat up as lost and are preparing expectations appropriately. No-one will be surprised if we win: we’re expected to.

It’s easy to say “by-elections don’t matter”. But the truth is that they often don’t matter – except when they do.

Here’s why Corby matters: what if we lose? That’s not to say it’s likely, but let’s think about that for a second.

Opposition parties usually have the upper hand at by-elections, for a start. For an opposition to drop two winnable seats in a row, both of which were thought to be shoo-ins, would raise some fairly serious questions about Labour’s readiness to win a general election. Sometimes pure sentiment can make a lot of difference in politics, and Labour needs to start looking like a winner.

Or rather, if we are serious about forming government in 2015, how could we not tip a 2,000 majority seat in our favour, under arguably the most favourable political circumstances in years, including a lead of roughly ten points in the polls?

There are three possible reasons which spring to mind:

The first is that there will be some kind of an upset no-one predicted, along the lines of Bradford West. It’s possible, but you need a fairly special seat in special circumstances for something like that to happen. People like Galloway are adept at finding such wildcard seats, but it’s hard to imagine that Respect would find fertile ground in Corby, or that there is another big enough minor party or single issue which could swing it. Highly unlikely.

The second is that there is an organisational failure. We also learned some lessons in Bradford West, and Iain McNicol is clearly a smart enough man to acknowledge mistakes and rectify them. Unlikely.

The third, following a process of elimination, would simply be that we find ourselves pathologically unable to translate highly positive political circumstances into totemic electoral triumph. That we might have a lead in the opinion polls, but that our message does not yet appeal to the precise voters of middle England which we need to be winning back. That we are still incapable of rainmaking, only of waiting for the Coalition’s bad luck.

In short, a loss in Corby begs the question: if not now, then when?

Now such an outcome is still unlikely: but what if it happened? The shock to Labour’s confidence would be huge. Not to mention its public standing.

According to Guido Fawkes, the venerable Tom Watson is “so obsessed with Corby he thinks it’s Ed’s Crewe”. Crewe, readers may remember, rather marked the point in 2008 where Gordon Brown’s honeymoon was well and truly over, and set the electoral tone for his ousting two short years later. It absolutely must not be Ed’s Crewe.

Whether Guido is right or merely gossiping, Watson would be absolutely right in treating the downside with that level of seriousness. A win is a necessary, but not a sufficient condition to get us on the road to 2015. This is a seat to be fought as if our very lives depended on it; and not just for the normal reasons of protecting against complacency and mobilising activists. It is because we cannot afford to lose.

Rob Marchant is an activist and former Labour Party manager who blogs at The Centre Left