How well does Labour need to do in the Corby by-election?

The party needs to win a majority of at least 12 per cent to match its current national poll lead.

Barring some dramatic upset, Labour will win today's Corby by-election (triggered by the resignation of Louise Mensch), gaining a seat from the Conservatives for the first time in this parliament. But winning alone isn't enough. A slender victory would prompt fears that the party still isn't where it needs to be if it's to stand a chance of winning the next general election. Thus, while Labour requires a swing (the rise in one party's vote added to the fall in another's and divided by two) of just two per cent to overturn the Tories' majority of 1,951, it needs a swing of at least five per cent to put it on course to win a national majority in 2015 and a swing of eight per cent to justify its average opinion poll lead of nine points. The latter would see it take the seat with a majority of around 12 per cent. 

To win Corby: Labour needs a swing of two per cent.

To win a majority in 2015: Labour needs a swing of five per cent to put it on course to win a majority at the next general election.

To match its national poll lead: Labour needs a swing of eight per cent to match its average national poll lead of nine points.

Polling by Lord Ashcroft in the constituency has suggested that Labour will easily exceed this benchmark. His final survey gave the party a lead of 22 points (with Labour on 54 per cent and the Tories on 32 per cent) and showed a swing of 12.5 per cent from the Tories to Labour.

Labour, naturally, has downplayed Ashcroft's findings, insisting that Corby will be "a very tough fight" in an attempt to ensure its supporters turn out. Ed Miliband reminded party workers last week that the party thought it had won in 1992 but ended up losing to the Tories by 342 votes. While history isn't likely to repeat itself today, anything less than a resounding victory in this mid-term electoral test will force Labour to ask why it isn't doing better.

Update: As the commenter below points out, there are two other by-elections today, in Manchester Central and Cardiff South and Penarth. Labour currently holds both seats by majorities of 10,430 and 4,709 respectively and is expected to retain them.

In addition, the first ever police and crime commissioner elections are taking place in 41 police authority areas in England and Wales. You can read my guide to the elections here.

Ed Miliband is hoping Labour can win a seat off the Conservatives for the first time since he became leader. Photograph: Getty Images.

George Eaton is political editor of the New Statesman.

Ukip's Nigel Farage and Paul Nuttall. Photo: Getty
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Is the general election 2017 the end of Ukip?

Ukip led the way to Brexit, but now the party is on less than 10 per cent in the polls. 

Ukip could be finished. Ukip has only ever had two MPs, but it held an outside influence on politics: without it, we’d probably never have had the EU referendum. But Brexit has turned Ukip into a single-issue party without an issue. Ukip’s sole remaining MP, Douglas Carswell, left the party in March 2017, and told Sky News’ Adam Boulton that there was “no point” to the party anymore. 

Not everyone in Ukip has given up, though: Nigel Farage told Peston on Sunday that Ukip “will survive”, and current leader Paul Nuttall will be contesting a seat this year. But Ukip is standing in fewer constituencies than last time thanks to a shortage of both money and people. Who benefits if Ukip is finished? It’s likely to be the Tories. 

Is Ukip finished? 

What are Ukip's poll ratings?

Ukip’s poll ratings peaked in June 2016 at 16 per cent. Since the leave campaign’s success, that has steadily declined so that Ukip is going into the 2017 general election on 4 per cent, according to the latest polls. If the polls can be trusted, that’s a serious collapse.

Can Ukip get anymore MPs?

In the 2015 general election Ukip contested nearly every seat and got 13 per cent of the vote, making it the third biggest party (although is only returned one MP). Now Ukip is reportedly struggling to find candidates and could stand in as few as 100 seats. Ukip leader Paul Nuttall will stand in Boston and Skegness, but both ex-leader Nigel Farage and donor Arron Banks have ruled themselves out of running this time.

How many members does Ukip have?

Ukip’s membership declined from 45,994 at the 2015 general election to 39,000 in 2016. That’s a worrying sign for any political party, which relies on grassroots memberships to put in the campaigning legwork.

What does Ukip's decline mean for Labour and the Conservatives? 

The rise of Ukip took votes from both the Conservatives and Labour, with a nationalist message that appealed to disaffected voters from both right and left. But the decline of Ukip only seems to be helping the Conservatives. Stephen Bush has written about how in Wales voting Ukip seems to have been a gateway drug for traditional Labour voters who are now backing the mainstream right; so the voters Ukip took from the Conservatives are reverting to the Conservatives, and the ones they took from Labour are transferring to the Conservatives too.

Ukip might be finished as an electoral force, but its influence on the rest of British politics will be felt for many years yet. 

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