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.

#Match4Lara
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#Match4Lara: Lara has found her match, but the search for mixed-race donors isn't over

A UK blood cancer charity has seen an "unprecedented spike" in donors from mixed race and ethnic minority backgrounds since the campaign started. 

Lara Casalotti, the 24-year-old known round the world for her family's race to find her a stem cell donor, has found her match. As long as all goes ahead as planned, she will undergo a transplant in March.

Casalotti was diagnosed with acute myeloid leukaemia in December, and doctors predicted that she would need a stem cell transplant by April. As I wrote a few weeks ago, her Thai-Italian heritage was a stumbling block, both thanks to biology (successful donors tend to fit your racial profile), and the fact that mixed-race people only make up around 3 per cent of international stem cell registries. The number of non-mixed minorities is also relatively low. 

That's why Casalotti's family launched a high profile campaign in the US, Thailand, Italy and the US to encourage more people - especially those from mixed or minority backgrounds - to register. It worked: the family estimates that upwards of 20,000 people have signed up through the campaign in less than a month.

Anthony Nolan, the blood cancer charity, also reported an "unprecedented spike" of donors from black, Asian, ethcnic minority or mixed race backgrounds. At certain points in the campaign over half of those signing up were from these groups, the highest proportion ever seen by the charity. 

Interestingly, it's not particularly likely that the campaign found Casalotti her match. Patient confidentiality regulations protect the nationality and identity of the donor, but Emily Rosselli from Anthony Nolan tells me that most patients don't find their donors through individual campaigns: 

 It’s usually unlikely that an individual finds their own match through their own campaign purely because there are tens of thousands of tissue types out there and hundreds of people around the world joining donor registers every day (which currently stand at 26 million).

Though we can't know for sure, it's more likely that Casalotti's campaign will help scores of people from these backgrounds in future, as it has (and may continue to) increased donations from much-needed groups. To that end, the Match4Lara campaign is continuing: the family has said that drives and events over the next few weeks will go ahead. 

You can sign up to the registry in your country via the Match4Lara website here.

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.