Five ways to win a referendum, and five potential pitfalls

David Cameron's new Conservative government is committed to a referendum on EU membership in 2016 or 2017. Many commentators assume that he will negotiate a package of EU reforms, cajole much of his party to back the result, and then cruise to victory in the referendum. And so he might. But there’s many a slip twixt cup and lip. How can Cameron maximise his chances of winning? And what are the chief obstacles that lie in his path?

Here are five pieces of advice for Cameron. First, he should not over-bid. Many Conservatives will urge him to ask for the moon. But if he tries to make fundamental changes to the EU, he will fail. Britain’s partners have no appetite for a new treaty, which would need ratification in 28 member-states, in some of them by referendum. Most capitals, including Berlin, fear that the lengthy process of changing the treaties would be like opening Pandora's box. There is no chance of a new treaty being ratified before the end of 2017. The best that Cameron can hope for is an agreement on minor treaty changes, to be ratified at some point in the future.

Second, Cameron must start making the case for EU membership. He did so with his Bloomberg speech of January 2013 – but never followed up, for fear of annoying Conservative eurosceptics and potential UKIP voters. Britain's partners will not take Cameron seriously until he is willing to explain to the British the benefits of EU membership – and thus to make enemies in his own party. Cameron must grasp the nettle that at some point in the campaign his party will split into two hostile camps, perhaps undermining its long-term cohesion.

Third, Cameron should take initiatives in the EU and seek to lead in areas where Britain has expertise. One reason why Britain's influence has waned in recent years is that it has often sat on the sidelines and appeared happy for others to lead. Britain's EU partners would listen to it with more respect if it made concrete proposals in areas such as foreign and defence policy, climate and energy, trade and the single market or co-operation on policing and counter-terrorism. They would welcome a more pro-active Britain.

Fourth, he must work hard at building alliances in the EU, where he has few good friends. When the European Council chose the new Commission president last June, only Hungary's Viktor Orban joined Cameron in voting against Jean-Claude Juncker. Angela Merkel is a friend on a good day, but she and Cameron are prone to misunderstand each other (as they did over Juncker's appointment). Other leaders sometimes complain that Cameron is a very transactional politician who does not invest sufficient time in building relationships. Britain's ties to the Central Europeans have frayed in recent years, partly because of the Conservatives' anti-immigration rhetoric. But the problem is not just the Conservatives. Under the last Labour government, too, many of the EU’s smaller members complained that British ministers and officials seldom took them seriously, for example by making the effort to visit them to discuss areas where they could work together.

Fifth and finally, clubs have not only rules but also mores. British politicians tend to forget that their rambunctious style of domestic politics – involving confrontation, bluntness and a win-or-lose psychology – goes down badly in Brussels. The EU works through long negotiations and compromises that end in everyone feeling that they have got something. Sometimes Cameron gets this: two years ago he worked patiently with Germany and other partners to forge a deal that shrank the EU budget. Sometimes he does not: during talks over the Commission presidency, Cameron told one leader that Juncker's appointment could prompt him to campaign to take Britain out of the EU. Such threats alienate potential allies.

Cameron is an intelligent, successful and – so far – lucky politician, who will probably get some of these things right. But as the last few decades of European history show, governments often lose control during referendum campaigns on EU issues. Here are five things that could go wrong.

First, Britain’s highly-charged debate on Europe may not only spur Conservative eurosceptics to demand reforms that are unattainable, but also damage the already tarnished British brand, and so make it harder for Cameron to clinch a good deal with his partners. In recent years, for example, sometimes hysterical press reports on EU immigrants have led many people on the continent to view Britain as a nasty country. The government's current refusal to take any North African boat people, and the prospect of Britain quitting the European Convention on Human Rights (so that it would join Belarus as the only European non-signatory) do nothing to help. The worse Britain’s reputation, the less likely are other governments – who all have their own domestic politics to worry about – to give Cameron what he wants.

The second reason to worry is that other EU leaders may not make significant efforts to help Cameron. True, they hope Britain stays in the EU. But Cameron has nothing to offer them in exchange for their concessions. Several governments have indicated that they will not agree to his probable demands and that if the British choose to leave, that is their problem. Madrid, Paris and Vienna are three capitals where there is not much sign of a willingness to accommodate British desires.

The third worry is that a flaming row over migration during the renegotiation may energise the get-out campaign. For Cameron, and many Britons, the priority will be to restrict EU immigrants' access to in-work and out-of-work benefits. Some of Cameron's demands challenge the fundamental EU principle of non-discrimination and thus require treaty change. But as my colleagues Camino Mortera and John Springford have written, Britain's partners are in no mood to indulge Britain on this. The danger is that Cameron raises the expectations of the British people on what can be achieved and then disappoints them.

A fourth risk is that the euro crisis turns nasty. Despite the eurozone economy's modest improvement this year, Greece's place in the currency union remains precarious. A Grexit could trigger panic in the financial markets and thus the need for emergency summits and improvised institutional repairs. If eurozone leaders – who are the same as EU leaders – are once again seen as economically incompetent, the EU's image in Britain will suffer. A new eurozone crisis would also divert leaders' time and energy from addressing British concerns.

A final concern is whether Britain's pro-Europeans can run an effective keep-Britain-in campaign. As in the EU referendum of 1975, much of the establishment is likely to support staying in. But the country has become less deferential since then. In Britain, as in much of Europe, the EU is disliked because it is seen as a project of the rich, successful, cosmopolitan and well-travelled elite. Pro-EU forces must marshal arguments that appeal to people who never went to university. A top-down, 'we know what is good for you' campaign could easily fail. But if Cameron keeps his demands modest, works on his relationships with other leaders and uses his fine skills as a salesman to make the case for the EU, the referendum is winnable.

Charles Grant is director of the Centre for European Reform.