Brexit: What Could Still Swing the Vote?

Two activists kiss each other in front of the Brandenburg Gate in Berlin, Germany, June 19. There's still much to play for in the final days before the U.K.'s Brexit poll. Hannibal Hanschke/Reuters

After months of passionate, sometimes bitter and sometimes downright shocking campaigning, Britain votes on Thursday on whether to remain a member of the EU or leave the bloc.

The campaigns will be going all out for the final days, hammering home the arguments on their strongest topics: the economy for "Remain" and immigration for "Leave."

But they'll also be at the mercy of events—as today's high-profile defection to the Remain side of former Conservative Party co-chairman Sayeeda Warsi shows.

So what will they be watching for? And what could influence the vote in the dwindling hours before Britain goes to the polls?

A lesson from history

As former YouGov President Peter Kellner has written, referendums in Britain tend to see a late swing to the status quo. Voters start to confront the hard realities of what they are voting for, and any potential risks get thrown into sharp relief.

If you ascribe to this theory, everything is playing out in textbook fashion. A long-held lead for "Remain" in the polls turned last week into an advantage for "Leave," but this weekend, several polls showed voters returning to the status quo. Initially, the thinking runs, voters knew very little about the EU (the issue has only been of pressing interest to obsessives previously in British politics). Then they began to learn more about it, and a well-run Leave campaign got them excited about the possibility of change. But now, the Remain camp's dire warnings on the economy are making them nervous.

By its nature, this theory involves a very late shift back to the pro-EU side, so we won't really know if it holds water until June 24.

Jumping ship

Warsi told The Times that she felt she could no longer support a campaign associated with "xenophobic" posters, citing the one unveiled last week by UKIP leader Nigel Farage. Her defection follows that earlier in June of Conservative MP Sarah Wollaston, a former GP, who had backed the Brexit campaign but said she had become convinced leaving the EU would damage the NHS.

The direct impact of such decisions on voters in the real world is likely to be minimal. Polls consistently show that politicians (and journalists, sadly) are less trusted on Europe than friends and family, and, in some cases, than high-profile figures such as business leaders or academics. The majority of voters probably won't even notice that this has happened.

But indirectly, such moves create chaotic press and draw the campaigns into dealing with process stories, robbing them of vital time to hammer home their key messages. Senior figures in the Remain campaign are coy this morning when asked if any more defections are forthcoming (which probably means they haven't definitively secured any yet). But another big shift either way could prove an unwelcome distraction.

Making your mind up

A report published by the Lansons consultancy released earlier in June found that up to 30 percent of people will change the way they vote or make up their minds in the week before the referendum. The Financial Times's poll of polls has undecided voters on 11 percent of the electorate, and many of the rest could still move before the day.

So how will they break? A London School of Economics (LSE) and Opinium survey published earlier in June found that Britons still undecided on how they will vote thought they would be £71 ($103) a year worse off if Britain voted to leave. That suggests there are significant obstacles for Leave in convincing these voters, especially since voters tend to focus on the real-world implications of their vote in the finals days before a poll.

But all is not lost for the outers. The Lansons research also highlights the responsibility as citizens that voters feel very strongly in the days before a vote. If Leave can hammer home the message that immigration poses a dire threat to Britain's security and wellbeing, and that a Brexit would change that, they might sway some people.

Unexpected acts

The death of Jo Cox, the Labour MP tragically shot and stabbed in her constituency last week, was a tragedy, and the analysis of its implications will extend beyond the referendum.

But in the immediate short term, some suggested it might push voters back towards "Remain," as they tire of the heightened emotions that the uncertainty of the referendum has unleashed.

There is little evidence for that, with most pollsters over the weekend pointing to other factors to explain swings back to a "Remain" vote: YouGov pointed to the economy, and Opinium's poll for the Observer was largely completed before Cox's death. But a ComRes poll for the Sunday Mirror found that responses to their pollsters which came in after news of Cox's attack emerged were markedly less Euroskeptic.

More broadly, however, the poll is liable to be influenced in the unfortunate event of another tragedy—be it a death, a catastrophic refugee incident, or a terror attack.