DAVID Cameron, the British prime minister, is heading to Brussels for a crucial summit with fellow European Union leaders later this week. He hopes to secure a deal that meets his demands for EU reforms in four specific areas. These are promises to improve EU competitiveness and promote free-trade deals; an end to Britain’s commitment to ever closer union; guarantees that countries in the euro will not discriminate against those (like Britain) that remain outside the single currency; and, most controversially, limits on in-work welfare benefits being paid to EU migrants into Britain. If he gets his deal, Mr Cameron will announce his plan to hold a referendum on EU membership in four months’ time, on June 23rd.

Mr Cameron is insisting that his deal will mean a big change in Britain’s relations with the EU, that it will have legal force and that reform will be a continuing process. He accordingly argues that Britain is better off staying in the EU and has even added that this matters for its security. His Eurosceptic critics, many of them in his own Tory party, dismiss his reforms as trivial changes that deliver neither the fundamental change in Britain’s relationship with the EU he once promised nor the full-on treaty change he said he would achieve. They also claim that, if it were once set free from the burden of EU red tape, Britain would be better off, and they insist that security is a matter for NATO and bilateral intelligence-sharing, not for the EU.

Once the referendum campaign begins, arguments over the significance of Mr Cameron’s reforms make will soon vanish. The debate will instead be on a deeper question: would Britain be better off in or out? It is a hard one to answer because nobody knows what exact relationship a post-Brexit Britain would have with the EU. Eurosceptics insist that Britain would continue to trade freely into the EU’s single market, which takes almost half of its exports, while escaping any obligations to stick to EU rules, to pay into the EU budget or to accept free movement of people. Their opponents say none of this will be possible, noting that Norway and Switzerland, two countries not in the EU that nevertheless have access to its single market, are required to observe all EU rules, to pay heavily into the EU budget and to allow free movement of people without having any voice in Brussels.

As with other referendums, this one will in the end be decided as much by fear of change as anything else. The uncertainty over what deal a post-Brexit Britain would secure, and the fact that undecided voters tend to opt for the status quo, ought to favour the campaign to remain in. Europhiles are already warning that the EU would not be generous in dealing with Britain should it choose to leave, and that Scotland might treat Brexit as an excuse to hold (and win) a fresh referendum on its independence. But Eurosceptics point to the advantages to their side from rising anti-immigration sentiment, from a feeling that the European economy is still in trouble and from a stridently Eurosceptic press. The latest opinion polls say the gap between stayers and leavers is narrowing which may be why Mr Cameron is so eager to get the referendum over with.