Ed Miliband knows that the Corby by-election is going to be a crucial test for his leadership. If he wins, it will be his first constituency gain since he became leader and serve a nicely timed blow to David Cameron’s autumn relaunch. Expectations are high: Bradford West aside, Miliband has managed to increase Labour’s share of the vote in every by-election held in this parliament so far. If he loses, it will be seen as a bitter blow: voters normally punish the party that caused an unnecessary by-election. With a slim majority of 1,895, the Tory candidate faces an uphill battle to hold the seat. If Labour can’t take Corby when the government is trailing 10 points in the opinion polls, it doesn’t bode well for the party’s ability to make gains in the 2015 general election.

This would explain why Miliband has already pounced; visiting the former steel town just three days after Mensch announced her resignation. He told local voters:

‘It’s going to be a tough fight. We’re going to fight for every vote. That’s why we’re here just three days after Louise Mensch announced she was standing down.’

The exact timing of the election will also be important for Miliband. If the by-election is, as strongly rumoured, held on the same day as the police and crime commissioner elections, both outcomes will be tied together. If Labour does well in both, it could be a double whammy for the party.

Corby’s mixed electorate presents a challenge for Labour’s candidate Andy Sawford. The seat consists of ex-industrial workers (on whom Labour will depend), and more rural constituents (who will look to the right). Labour will have to appeal across both categories, as Miliband acknowledged in his speech.

But Labour isn’t the only party keeping a close eye on the by-election. There have been murmurings of James Delingpole — of this parish — running for UKIP. In a blog sounding out opinion, Delingpole says he’d ‘love to do my bit in parliament to help Chris Heaton-Harris MP with his campaign to stop this gorgeous and much-underrated county becoming the wind farm capital of Britain’. But do UKIP have much of a chance of making an impact in Corby? Take a look at how they’ve done in recent elections:  

The results suggest that UKIP voters, who are supposed to be disenfranchised Tories, are few and far between in Corby. The party didn’t even stand a candidate in 2010. Any impact they can muster would be minimal, beyond the publicity that comes with by-elections.

If the national opinion polling is correct, it will be the Lib Dem vote that collapses and is redistributed to Labour. It is going to be a closely-watched fight that will set the political tone for 2013. The timing of Mensch’s resignation  is extremely bad for the Tories, but given recent economic news she knows when to leave a party. Combined with his early visit, it looks like Miliband will seize the upper hand.

Tags: By-election, Ed Miliband, James delingpole, Louise Mensch, UK politics, UKIP