Polling 12 April 2021 If Labour loses Hartlepool, which of its MPs are in danger of losing their seats? Fourteen current Labour MPs, including Ed Miliband, Yvette Cooper and Ian Lavery could be at risk. Stefan Rousseau-WPA Pool/Getty Images Keir Starmer meets local people in Seaton Carew in County Durham, during a day of campaigning for the Hartlepool by-election Sign UpGet the New Statesman\'s Morning Call email. Sign-up On 6 May, Labour may lose the seat of Hartlepool, in a by-election being held on the same day as the local elections. If Labour does lose – as seems quite possible, both in theory and if we pay attention to (somewhat unreliable) constituency polls – there are 14 other Labour seats, mainly in the north, which are theoretically at-risk in a future national election. These 14 seats are held by some of the most prominent MPs in the Labour Party. The endangered MPs include: Ed Miliband, the shadow business secretary; John Healey, the shadow defence secretary; Ian Lavery, the former party chairman; Rosie Winterton, the former chief whip; Jon Cruddas, the former party policy chief; Jon Trickett, the former shadow minister; and Yvette Cooper, the former secretary of state. [See also: A shock poll from Hartlepool is less revelatory than it seems] Why are these MPs – and seven others, including Zarah Sultana – at risk if Labour lose Hartlepool? Because the 2019 election was arguably even worse than it appeared for Labour. The scale of their collapse in what were once “heartland” seats across the north was cushioned then by the presence of the Brexit Party. The Brexit Party did not stand in many Tory-held seats, but it did in many Labour-held ones, including Hartlepool, where it polled 25.8 per cent – its third-best result nationally. (The party polled over 10 per cent in 37 seats, 34 of which were held by Labour.) One of the most important electoral questions in politics is what happens to that Brexit Party vote at the next election. The Brexit Party only polled 2 per cent nationally in 2019. If its vote has split, say, 2:1 to the Tories over Labour, it would add half a point to the Conservatives’ national poll lead. Any evidence of how it has split is, therefore, naturally hard to discern in such polls. The great benefit of the Hartlepool by-election is that there is a great deal of 2019 Brexit Party vote set to be reapportioned between the major parties. Hartlepool will therefore give us a sense of whether these 14 other Labour MPs are also in danger: one would expect the 2019 Brexit Party vote to split in a fairly similar manner across all 15 of these seats. If one averages the two constituency polls held in Hartlepool so far, the Conservatives have a two-point lead. We should be wary of putting much faith in local polls, but a very close race would make sense. [See also: Labour’s selection in Hartlepool is a familiar story – with a new risky context] Why? Because if you split the 2019 Brexit Party vote in Hartlepool by 2:1 to the Tories over Labour, and hold all other aspects of the 2019 result equal, the two parties would be tied in the seat. In other words, a slim Tory lead here suggests a slightly-better-than 2:1 split of the Brexit Party vote (putting aside minor shifts in other vote shares; there are few Lib Dem or Green voters in Hartlepool). The calculation is simple and imprecise – it will not be wholly accurate – but it should serve as a good approximation of which Labour MPs are at-risk of losing their seats. Miliband, Healey, Cooper, Winterton, and Trickett (as well as Toby Perkins, Alex Cunningham and Karl Turner) are all at-risk because of a significant 2019 Brexit Party vote in their seats. The Brexit party polled 20.4 per cent in Miliband’s seat of Doncaster North, for instance – a seat he retained by a relatively slim margin of 5.8 per cent. Others, such as Cruddas and Sultana, as well as Mohammad Yasin, Taiwo Owatemi and Mark Tami, are at-risk under this model because their 2019 majorities were so slim. The Brexit Party vote in their seats ranges from only 2 to 7 per cent, but splitting the vote 2:1 in favour of the Tories would imperil them all, holding other vote shares equal. (If in fact Labour take a few points from the Lib Dems at the next election, as current polls suggest, then a few of these MPs may retain these seats.) By-elections matter. In 2017, the Tories won the northern seat of Copeland from Labour for the first time since its creation in 1983. The Tories retained it shortly afterwards in the 2017 election and in 2019 greatly increased their majority there. The initial by-election signalled the post-2016 referendum shift away from Labour in such seats. Hartlepool may soon prove to be a similarly stark forewarning for the Labour Party. [See also: Why being boring might be an advantage for Keir Starmer] › Why the BBC’s wall-to-wall coverage of Prince Philip’s death was a mistake Harry Lambert is special correspondent at the New Statesman and writes long reads. He tweets at @harrytlambert. Subscribe For daily analysis & more political coverage from Westminster and beyond subscribe for just £1 per month!