A Union Jack flies next to European Union flags ahead of a January visit by British Prime Minister David Cameron at the European Commission in Brussels. (Laurent DuBrule/ European Pressphoto Agency)

Will Britain stay in the European Union?

For decades Euroskeptics in the Conservative Party have criticized E.U. membership. They lambast what they see as interfering regulations on business, the erosion of parliamentary sovereignty and uncontrolled migration from other E.U. member states. So, in an attempt to keep his Conservative party together, Prime Minister David Cameron promised a renegotiation of Britain’s membership followed by a referendum.

Right now, it looks as if Britain will vote on continued E.U. membership in June. Following a frantic period of shuttle diplomacy, earlier this month Cameron announced the outlines of a deal between the United Kingdom and the other 27 E.U. member states about the terms of British membership. Cameron hopes to finalize the agreement at an E.U. leaders summit on Feb. 18 and 19, paving the way for a referendum this summer.

Six factors are central to whether Britain will remain in the European Union.

1. David Cameron’s elaborate game of persuasion 

Cameron is in an elaborate two-level game. At the first level, he needs to persuade his fellow E.U. heads of government to agree to a deal. While most of them want the U.K. to stay inside the club, other E.U. leaders resist some of Cameron’s demands, particularly the plan to restrict benefits to E.U. citizens working in the U.K. Nothing is agreed until everybody agrees at E.U. summits.

So, in exchange for supporting any deal, one or more heads of government will probably try to extract a side concession or two on something largely unrelated to British membership, designed to reward a politically important group or lobby back in their own country. At best, that might lead to a delay until a further E.U. summit; at worse it might unravel the entire deal.

At the second level, once a deal is signed, Cameron will have to persuade British voters. The choreography includes the shuttle diplomacy, the E.U. summit, and in recent weeks, hints that he might not sign a deal if the rest of the E.U. didn’t make enough concessions. All this has been designed to convince British voters that Cameron extracted some meaningful concessions. He’s trying to spin a narrative of hard-fought and significant success.

2. Conservative Party unity

Publicly, Cameron has said that the referendum’s goals were to defend national interests and to give the British people a say over E.U. membership. But when in 2013 Cameron first pledged to hold a referendum on E.U. membership, he was trying to ensure that the Conservative Party’s internal differences about Europe wouldn’t dominate the run-up to the May 2015 election.

Several rank-and-file Conservative MPs will campaign to leave the E.U. But the “leave” campaign hopes to gain a bigger political star. According to recent speculation, Justice Secretary Michael Gove, Home Secretary Theresa May, London Mayor Boris Johnson and other cabinet ministers might campaign for exit.

They might do so to boost their own chances of becoming prime minister when Cameron steps down. Being a figurehead for the “leave” campaign might demonstrate courage and curry favor with the traditionally Euroskeptic Conservative party membership.

However, recent research by Queen Mary University of London’s Tim Bale and colleagues suggests that most ordinary party members will decide on the basis of the final terms of the deal Cameron will strike in Brussels.

3. A referendum on Brexit — or on Cameron and his government?

One question may be on the ballot paper, but voters will use the referendum to express their frustration with the government in power. That, at least, is what we’ve seen in E.U. referenda across Europe. This referendum is closely associated with Cameron himself, especially since he’s the one striking the deal with fellow E.U. leaders.

The main opposition Labour Party may overwhelmingly favor remaining in the E.U., but traditional Labour voters may be far less inclined to go to the polls to vote for Cameron’s deal.

Cameron announced before the last election that he would step down at the end of this term. Defeat in the referendum would, almost certainly, prematurely end Cameron’s time in Downing Street. Knowing that the fate of Cameron is linked to success or failure might persuade some of his opponents within his own party to vote to leave in order to remove him from office.

4. Public opinion can be fickle

Cameron has outsourced the final decision of Britain’s membership of the E.U. to the vagaries of a referendum campaign. Public opinion, perhaps fueled by press criticism of his draft deal, appears to be moving toward exit.

But public opinion is fickle. Once the campaign proper begins, that trend could quickly reverse especially when a succession of moderate politicians and business leaders start warning voters of the fearful unknowns associated with leaving the E.U.

British voters are among the most Euroskeptic in the E.U. But except for a few diehard Europhobes, the vast bulk are what Sussex University’s Paul Taggart and Aleks Szczerbiak dub “soft eurosceptics.” They don’t much like the E.U., but neither is it high on their priority list. Much may depend, therefore, on how well the “remain” campaign is able to mobilize lukewarm voters on referendum day.

5. ‘Events, dear boy, events’

When asked by a reporter what was the biggest challenge facing him, a former Conservative prime minister, Harold MacMillan, is reputed to have said, “events, dear boy, events.

Given how fluid public opinion can be, the result may depend on any number of outside events. Another large influx of migrants into Europe, a terrorist attack, a downturn in the world economy, a sharpening of the euro-zone crisis, even bad weather on polling day: Any of these could prove decisive.

If the referendum is on June 23, as now widely expected, the fate of Britain’s membership in the E.U., as Sussex University’s Dan Hough noted, could even depend on how well England perform in the European soccer championships: They face a potentially decisive game against Slovakia just three days before.

England’s departure from the European championships could increase the chance of Britain’s departure from the E.U.

6. Timing

Timing could be crucial. Cameron is keen to hold the referendum sooner rather than later. He wants his government to devote more time to other issues and to put to bed the divisions in his party. The later the referendum, the more Euroskeptic Conservatives will develop the habit of criticizing their leader publicly and the more likely an unexpected event might derail the campaign.

Scottish First Minister Nicola Sturgeon has criticized the possibility of a June referendum. She complained that a June vote would interfere with the elections to the Scottish parliament in May, essentially arguing that the U.K. isn’t giving Scottish elections due respect.

That’s a strategic move. Here’s why. Scots will vote to remain. If the rest of the U.K. overwhelms them and votes to leave, she can argue that London doesn’t really care about Scotland and then push the case for another referendum on Scottish independence, which the nationalists would almost certainly win.

Cameron’s decision to make his referendum pledge was a gamble designed to help win the 2015 British general election. He has now mortgaged his future and the future of Britain’s place in Europe on the referendum’s outcome. The referendum could lead to Britain’s break from the E.U., the breakup of the Conservative party and even the breakup of the United Kingdom. The stakes couldn’t be much higher.

Tim Haughton is associate professor of European politics at the University of Birmingham and has been the co-editor of the Journal of Common Market Studies Annual Review of the European Union since 2008.