As the negotiations to exit the European Union proceed, pressure will increase on the Labour party to adopt a firmer stance regarding their support or opposition to Brexit, or at least support for a softer form of Brexit such as remaining in the single market and customs union.

During the 2017 election, Brexit policy occupied a back seat for Labour, and indeed this didn’t appear to be a key issue in the forefront of Labour voters minds, unlike the Conservatives in which Brexit was the most important issue. What did appear clear however, is that the Liberal Democrat and the Greens Party policies of reversing Brexit didn’t help their performance, who lost many voters to the Labour party despite the former gaining some seats.

The danger for Labour not adopting a closer relationship with the EU is obvious, due to the recent influx of younger people who mostly voted to Remain in the EU, the original official Labour position during the referendum campaign. Even before the General Election, 63% of Labour voters voted to Remain, and the same percentage recently said they would be delighted or pleased" if the party came out against Brexit, with 22% saying they would feel the same if it vowed to go ahead with leaving the EU. However, these figures only refer to current Labour supporters. This says little about the voters Labour need to form a majority, most of whom voted to leave, and still support Brexit.

Therefore, the best political policy for Labour is far from clear, and this might explain their ambivalent attitude to the Brexit issue. Unlike the Conservative and Liberal Democrats who appear constrained to support their respective positions for and against Brexit, Labour have greater flexibility to change policy as the date for leaving the EU approaches. This will be particularly beneficial if severe problems arise, and if another General Election is in the offing.

In an attempt to gain some objective evidence how Brexit policy might affect Labour and Conservative support, this analysis examines how a more polarised viewpoint on Brexit would influence seats for both parties, using EU referendum and General Election data on each constituency.  In other words we assume constituents who voted Leave and for Labour last time would turn to the Conservatives, and those who voted Remain and Conservative last time turn to Labour. This might happen if Labour decided to choose a soft Brexit or a second referendum.

Two scenarios are illustrated in figures 1 and 2 respectively.

1) For every 4 points a constituency voted leave greater than the average of 52 percent for the country, the Conservatives gain one percentage point and Labour lose one percentage point in vote. This is a 1/4 or 25% weighting. Also the reverse applies to the same extent, so that for every 4 points a constituency voted leave less than the average of 52 percent for the country, Labour gain one percentage point and the Conservatives lose one percentage point in vote.

2) as in 1), but using a lower weighting of 1/10 or 10% so the polarising effect of Brexit on party vote is less extreme.

All the Labour, SNP, Liberal Democrat, Green and Plaid Cymru seats have been summated into a post election ‘Labour Alliance’. However, this doesn’t substantially influence the change of vote for the Labour party if this is counted separately, since it’s assumed the size of the popular vote for the other parties remain unchanged.

The results for the referendum 52/48% result can be seen by moving up and down the y axis in figures 1 and 2. In the 25% weighting or high Brexit influence scenario, the Conservatives gain 14 seats and the Labour alliance lose 14 seats. In the 10% weighting scenario or low Brexit influence scenario the Conservatives gain 5 seats and the Labour alliance lose 5 seats. It should be emphasised this adopts a neutral stance on Brexit overall, only the individual constituencies are affected.

These, scenario's can then be applied to examine the effect of a national swing in sentiment for Brexit on party seats away from the 52%/48% leave/remain result, between 39%/61% leave/remain, and 59%/41% leave/remain, for each percentage point. These are shown by the red line for the Labour alliance and blue line for the Conservatives.

To merely achieve the same result as in the 2017 General Election resulting from polarisation of Brexit views, the Labour Alliance would require a shift in Brexit sentiment to 45.5% Leave/54.5% Remain in the 25% weighting scenario, and 47% Leave/53% Remain in the 10% weighting scenario.

Of course this assumes everything else remains unchanged. Brexit was a less important issue for many Labour voters, than Conservative, UKIP and Liberal Democrat voters, and polls indicate that Labour have gained share since the 2017 election. There are of course many other scenario’s, such as Labour voters changing to the Liberal Democrats in the event that their stance on rejecting a hard Brexit isn’t strong enough, or Conservative voters changing to UKIP if their stance supporting a hard Brexit weakens. The latter would be particularly damaging for the Conservatives, (and beneficial for Labour) which explains why they are constrained to this policy, irrespective of any problems which lie ahead. Whilst the dangers of Brexit are evident for Labour, they have slightly greater flexibility to change policy if national sentiment towards Brexit changes. Brexit policy, therefore provides considerable danger to both parties. This might also explain why Labour are reluctant to get involved to being committed to a firm policy at this stage.

In conclusion, if any further weight is given to Brexit issue by voters, the effect is disadvantageous for Labour in terms of seats. This isn’t surprising since 70% of Labour seats voted for Leave and many of these are marginal Labour seats. In contrast Labour support is larger in many areas which voted Remain, but these provide little extra benefit in terms of political power in our first past the post system. What polls often ignore, is that it isn’t the typical voter for a party that matters but the marginal voters who may have very different attitudes.

Labour therefore faces a dilemma whether to support Brexit to avoid losing, or failing to gain marginal seats, or possibly losing or failing to gain less marginal seats if far greater numbers of Remain voters desert them. The safest scenario for them would be if there was large change of national sentiment to remaining in the EU, or a soft Brexit, and then adopting an pro EU, or 2nd referendum stance. Of course unless there are severe difficulties arising before we leave the EU leading to a General Election, all this will be somewhat academic.