The Spill-Over Effect: Brexit and Prospects for Westminster

Posted on 6 June 2019 by John Curtice

Today’s Westminster by-election in Peterborough is taking place in the immediate wake of a Euro-election in which voters left both the Conservatives and Labour in droves, switching instead to parties that were backing clearer if more polarising options on Brexit. The timing of the by-election thus switches our attention rather rapidly towards what might be the fallout from the Euro-election for the parties’ Westminster prospects.

Three polls of Westminster vote intention have been conducted and published since the Euro-election results were unveiled. With one poll putting the Brexit party ahead, and another suggesting the Liberal Democrats are in front, they hardly suggest that the Euro-contest has left the regular rhythms of Westminster politics undisturbed. Indeed, rather than looking like a two-party system, they suggest that British politics now resembles more of a four-party one, with, on average, the Brexit Party on 25% narrowly ahead of Labour on 22%, while both the Conservatives and the Liberal Democrats are not far behind on 19% apiece. Meanwhile, the Greens have also registered a respectable 8%.

These figures are not simply a flash in the pan. That the Euro-election was having a knock-on effect on voting intentions for Westminster was evident well before the ballot boxes were opened ten days ago. At the beginning of April, when the prospect of the Euro-election first came into view, Labour were on average on 34% in the polls, four points ahead of the Conservatives on 30%, while UKIP and the (yet to be formerly launched) Brexit Party enjoyed 11% support between them, and the Liberal Democrats just 9%. However, by the time we had reached the week before Euro-election polling day, polls of Westminster vote intention were putting Labour down at 30% and the Conservatives on 25%. Conversely, they reckoned the Brexit Party was now on 18%, while the Liberal Democrats’ support had risen to 13%.

In short, the standing of the Brexit Party and the Liberal Democrats in the latest Westminster polls does not simply represent a reaction to the outcome of the Euro-election. There was already clear evidence before the result was known that the Euro-election was having a spill-over effect.

That said, the success of the Brexit Party and the Liberal Democrats (and indeed the Greens) in that election has evidently pushed yet more voters in their direction than was the case immediately before polling day. Some of the support that they are registering in the latest Westminster polls may therefore represent little more than a reaction to favourable publicity

We might note too, that even the latest polls of Westminster vote intention do not put any of the Brexit Party, the Liberal Democrats or the Greens in as strong a position as they achieved in the Euro-election. The spill-over effect evidently has its limits, and not all those who voted for these parties a fortnight ago would do the same thing in a general election, when the ties of traditional party loyalty are likely to prove stronger than they did in the Euro-poll.

Meanwhile, this year’s Euro-election is far from being the first to have had a spill-over effect. The Greens’ success in winning 15% of the vote in the Euro-election in 1989 saw the party rise from not being identified separately in the polls to registering 9% in Westminster vote intentions. UKIP’s success in coming second in the 2009 Euro-election was accompanied by a doubling in the combined tally for Others (a tally that includes UKIP) from 10% at the end of March to 20% in the fortnight or so after the election. Interestingly, UKIP’s subsequent success in coming first five years later had less of an effect, though the party’s average support still edged up from 12% in the last week of March 2014 to 16% at the time of the Euro-election.

Past experience suggests that much of the sudden boost that a party secures on the back of a strong Euro-election performance can disappear within a matter of months. By the end of 1989 support for the Greens had fallen back to 4%. The combined tally for Others was back down to 12% by mid-October 2009. Even the relatively modest growth in support for UKIP in 2014 had eased somewhat by the end of July that year, with the party by that point running at 14%.

So, should we expect the spill-over effect of the European election to melt away in the heat of summer, as memory of the outcome begins to fade? Not necessarily. For there is a vital difference between the most recent Euro-election and its predecessors. The principal reason for the success of the Brexit Party, the Liberal Democrats and the Greens and the collapse of the Conservatives and Labour in this year’s contest – the Brexit debate – is not going to disappear from the political agenda any time soon. Rather, voters are going to be reminded continuously of the arguments that impelled them to vote in the record-breaking way they did in the Euro-election.

Indeed, the role that Brexit has played in reshaping voters’ Westminster preferences, and not just those that were expressed in the Euro-ballot boxes, is quite clear in the latest polls. Nearly all the support for the Brexit Party in Westminster vote intentions comes from those who voted Leave, nearly half of whom (on average, 47%) say they would vote for Nigel Farage’s party in an immediate general election. Equally, nearly all the support for the Liberal Democrats (and all of the increase in their support since early April) comes from those who voted Remain. Indeed, following upon the Liberal Democrats’ success in coming first in the Euro-election among those who voted Remain, it appears that the party is now also challenging Labour for the title of the most popular party for Westminster among Remainers, with (on average) 33% of them currently supporting the Liberal Democrats and 31% backing Labour’.

In short, support for the Brexit Party and the Liberal Democrats has none of the hallmarks of an inchoate protest vote against the traditional two-party system. Rather, it appears to reflect the very distinctive views of voters on opposite sides of the Brexit debate, a debate that seems set to dominate the political agenda for the foreseeable future. In contrast, both Labour and the Conservatives, more comfortable as they are with the politics of left and right than the debate between social liberals and social conservatives that underpins Brexit, find themselves trying to straddle the Brexit divide. Though the Conservatives are more popular among Leave (25%) than Remain voters (13%), a pattern that does contrast with the position in the Euro-election, it is still among this group that the party has lost most ground since Mrs May first unveiled her deal last November. In the case of Labour, which enjoys just 12% support among those who voted Leave, the balance of support for the party is (as in the Euro-elections) in the opposite direction.

As a result, the difficulties the Conservatives and Labour faced a fortnight ago in trying to hold their electoral coalitions together are also clearly in evidence in the battle for power at Westminster. The Conservatives’ principal problem, by far, is that as many as 40% of those who voted for the party in 2017 now say they would vote for the Brexit Party in a Westminster contest. Labour, which has lost 11% of its support in that direction, is not immune to the challenge from that quarter either, but the party’s losses in that direction are heavily outweighed by the 19% of the party’s vote that has switched to the Liberal Democrats and 11% that has moved to the Greens. How these parties resolve the internal debate about Brexit currently raging within them could well play a vital role in determining whether the challenge they now face as a result of Brexit does eventually melt away or not.



John Curtice

By John Curtice

John Curtice is Senior Research Fellow at NatCen and at 'UK in a Changing Europe', Professor of Politics at Strathclyde University, and Chief Commentator on the What UK Thinks: EU website.

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