Why might Labour MPs support Theresa May’s Brexit deal? Part 1 – the Inbetweeners

by Stephen Fisher and Eilidh Macfarlane.

If the prime minister passes her Brexit deal it will be with the votes, or at least abstentions, of some Labour MPs. It is commonly accepted among commentators that even if she manages to persuade the DUP and more Conservative MPs, there will be some who never will. So she will need support, or at least co-operation in the form of abstention, from Labour MPs.

John Rentoul has compiled a list of those who might be willing. The list might not be perfect, but we use it as indicative of the kinds of Labour MP who might be won over. We refer to those on the list as the potential deal backers.

This group also matters because, as Stephen Bush said, not only are those 30 or so Labour MPs not currently enough to enable May’s deal to pass but their “existence makes it near impossible to see how a second referendum will happen.”

The purpose of this blog is not to try to predict whether, how many, or which Labour MPs will or won’t block a second referendum or help the prime minister pass her deal. It is to discuss some of the reasons why they might be tempted to back the deal in order to say something ex ante about what, if it does come to pass, will be heavily analysed ex post.

Although we discuss normative principles, we are not making an argument as to what Labour MPs should do. To the extent that we have a conclusion it is that there are numerous conflicting factors Labour MPs have to take into account. Whatever they decide to do they will be able to point to a rationale that is defensible. Since we cannot look into their heads or hearts we will never know for sure why they behaved as they did, and even MPs themselves may not be certain which of the many and competing motivations facing them was decisive.


Most Labour MPs voted Remain but represent Leave voting seats. These MPs are sometimes referred to as ‘inbetweeners’. As the table shows, most of the MPs thinking of backing the deal fall into this category. The few who voted Leave in the referendum are mainly on the potential backers list, apparently regardless of how their constituency voted. However, the group that are most likely to prove pivotal for a Brexit deal are those inbetweeners who are also potential deal backers.

Table 1. Labour MPs by Constituency, Personal Referendum Vote, and willingness to back May’s Deal

  MP voted Leave MP voted Remain
Constituency: Potential deal backer Not Potential deal backer Not
voted Leave 3 1 28 121
voted Remain 2 1 3 98

Note: This table is based on John Rentoul’s list of potential leave backers, and the best information we could find on the referendum vote choice of those Labour MPs newly elected in 2017. Votes for others come from the BBC.

Even though less than 20% of inbetweener Labour MPs have signalled that they might back May’s deal, it is somewhat inevitable that the inbetweeners should be the biggest group of potential deal backers. 97% of Labour MPs voted Remain, but 60% of Labour constituencies voted Leave.

On average Labour MPs are broadly in tune with Labour voters, 69% of whom voted Remain. The disjuncture arises because Remain votes and Labour votes are concentrated in big cities, especially London, where there was a big majority for Leave. Outside London, fully 71% of Labour constituencies voted leave.

Many commentators seem to readily accept that inbetweeners are inevitably conflicted but it is not clear what the nature of that conflict is.

The simple disjuncture is not enough. Few argue that Leave voting MPs in Remain seats ought to vote against Brexit in parliament. Given it is the overall referendum result that matters then the question is whether all MPs should back the deal to deliver on the referendum, regardless of the referendum result in their constituencies.

Party matters here because the Labour manifesto accepted the referendum result while the Liberal Democrats, Greens, and Scottish and Welsh Nationalists did not. Since the 2017 general election there has been pressure on Labour MPs to back the deal because of their manifesto commitment, and this is something that many inbetweeners who are also potential deal backers have referred to. For example, Caroline Flint who backed the Deal at the last meaningful vote on the 12thMarch, wrote “I campaigned for Remain, but I promised at the 2017 general election, in line with Labour policy, to honour the outcome of the 2016 referendum.” Given that all Labour MPs stood for election on this platform, why is it that this pledge is pressuring those in Leave voting constituencies particularly?

Of the inbetweener potential deal backers, Stephen Bush has said that they“don’t want Brexit to be stopped and fear that anything which looks like stopping it will cost them their seats.” Historically, how MPs have voted in parliament, even on the big issues of the day, has not affected their electoral performance much. The appendices to the Nuffield Election Studies by John Curtice and his colleagues have occasionally evaluated whether constituency level vote share changes differ according to which way MPs from the same party voted on particular issues. They find that differences are small if they exist at all. These include analyses of the effects of voting on the Iraq war, and on tuition fees, on Labour party performance at the 2005 election; and the experience of Liberal Democrat rebels in 2015. It is also true that the severity of the expenses crisis claims did not affect constituency outcomes much in 2010. Most recently, Chris Hanretty, Jon Mellon and Patrick English have argued that MPs were not punished or rewarded much for their Leave/Remain referendum vote at the 2017 election. On that basis, MPs should not think it matters much for their particular chances of re-election which way they personally vote on the deal, as opposed to which way their party votes and how their party comports themselves.

But even if MPs do believe that how they vote will make a difference for their electoral performance, it is not clear that inbetweener Labour MPs would be increasing their chances of re-election if they voted for the deal.

The YouGov MRP model estimates suggestthat nearly all Labour MPs were elected by voters who predominantly support Remain. That is to say that in a three-way contest between Remain, May’s deal and no-deal, Remain would be both the plurality and Condorcet winner among the Labour voters in each Labour constituency.

Maybe inbetweener Labour MPs are worried about Leave voters who voted for other parties in 2017 ganging up on them, perhaps with a tactical squeeze in favour of the leading alternative candidate. But coordination among voters for other parties alone can only unseat an MP if that MP commands less than half the votes in the constituency. That was the case at the last election for only 5 out of the 28 inbetweener potential deal backers. Similarly, only 5 of them won with a margin of victory of less than 10 percentage points. Most are in relatively safe seats. What’s more there is no apparent correlation between the margin of victory and the willingness of inbetweener MPs to signal a willingness to back the deal.

Maybe it is not a question of inbetweeners being at risk of losing their seat but instead a question of representation. Some appear to argue that MPs should vote as their constituencies did. We only have estimates (thanks to Chris Hanretty) not actual figures for the referendum results by constituency, but that is by the by. More importantly, the implicit principle does not work. Sometimes the majority of constituencies vote in the opposite direction from the country as a whole, as in the 1951 general election. The 2016 referendum result was not far from a narrow vote for Remain. Had the Remain vote been a bit higher everywhere, then a majority of seats would still have voted Leave even if Remain had won overall. It is not coherent to suggest that the overall results of referendums should be respected and also that MPs should vote according to how their constituents voted on subsequent referendum legislation.

Many of the inbetweener potential deal backers are in seats where the Leave vote was so big that perhaps there is a case for representation for a strong constituency mood so long as it is in agreement with the overall result. This is something several potential deal backers have stressed. For instance, Sarah Champion wrote in her local newspaper, “as Rotherham’s Member of Parliament, it is my duty to represent the views of the people of Rotherham. This is something I take incredibly seriously. Rotherham voted, overwhelmingly, to leave the European Union. I respect this decision. I therefore have no intention of seeking to block Brexit, or to try to reverse the result of the 2016 referendum.”

The Leave share of the vote in Rotherham is estimated to have been 68%. That is high. But the average Leave share in constituencies with potential deal backing inbetweener Labour MPs is, at 64%, only a bit higher than the 59% average for inbetweener seats generally. Some of the inbetweener potential deal backers are in seats with relatively modest Leave leads. Nonetheless, inbetweener Labour MPs are more likely to have signalled willingness to back the deal if they serve seats with more Leave voters.

While representing overwhelming opinion is understandable, it is worrying when some people try to overwhelm MPs with their strong opinions. Threats to MPs are serious and frequent. Some Remain supporting MPs have changed their position on key Brexit votes as a result of the abuse and threats they have received according to Harriet Harman. We do not know if this extends to any inbetweener MPs signalling willingness to back the deal because of threats. Nor do we know if the level of threat faced by inbetweener MPs is correlated with the Leave share of the vote in their constituencies, but it would not be surprising if it was.

Despite much discussion of MPs needing to be responsive to their constituencies, just 20% say they their MP should consider what people in their constituency want when voting on the Brexit deal. Instead people mainly want MPs to consider what is in the national interest. What that means, and what it means to honour the referendum result, will be the subject of the second part of this blog.

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