Britain is hurtling along the road to a European exit In promising a referendum David Cameron signposted the route for Britain's departure from the EU. Unsurprisingly, a deeply eurosceptic Conservative party is now unceremoniously bundling the prime minister along this path. Exit has long been a plausible outcome of the endless Tory paroxysms. It has begun to look a probability. This is a sobering thought, and not only for foreign investors thinking about where to put their money. When Harold Wilson gave Britons a plebiscite on EU membership in 1975 the then British leader was not thinking about the national interest. He wanted to bridge divisions in his own, half-sceptic party. A sham renegotiation to secure better membership terms was followed by a government call for a Yes vote. Wilson won the day, and, for a time, quelled the anti-Europe rebellion. Faced with his own eurosceptic insurgency, Mr Cameron imagined he could pull off a similar coup. The realities of coalition politics with the Liberal Democrats precluded an immediate referendum, so he promised a vote if the Tories won the 2015 election. The ploy, quite predictably, has failed. Sceptics have learnt a lot since 1975. They have been emboldened rather than placated by the referendum pledge. As was evident during his talks this week with Barack Obama at the White House, on the question of Europe the prime minister is in office but not in power. A prominent, Conservative-minded commentator describes him as the "bullied child in the playground." However many sweets he hands his tormentors, they want more. Mr Cameron interrupted his US trip to rush out a draft of his proposed referendum bill. The sceptics demanded more. The present condition of the Tories invites a second parallel, this time with the left of the Labour party during the early 1980s. Defeat at the hands of Margaret Thatcher in 1979 shattered Wilson's truce. Labour fought the 1983 election on promises to quit the EU, scrap Britain's nuclear weapons and nationalise the banks and much of industry. When Thatcher won a bigger majority the left, bizarrely, claimed that this was because Labour's prospectus had been insufficiently radical. The same surreal absolutism now energises the eurosceptic right. It is true that British voters have never been enthusiasts for Europe. They have scarcely been won over by the crisis in the eurozone. The immigration associated with the EU's eastern enlargement has been exploited by the populist UK Independence party. The narrative peddled by Ukip - Britain's troubles are all the fault of outsiders - has resonance in tough economic times. For their part, Tory sceptics hum a curiously defeatist tune: Britain is doomed forever to be the victim, rather than a leader, in Europe. They are reading, though, only one side of public opinion. While most voters do not much like Brussels, they are not obsessed by it. When they are asked to rank the EU in the list of things most salient to their daily lives, it rarely makes the top 10. Most people have more pressing concerns such as living standards and jobs, hospitals and schools. The next demand of the Tory sceptics will be that Mr Cameron set out his demands for the promised renegotiation with Britain's partners. He must spell out precisely which powers will be repatriated to the Westminster parliament, which EU policies Britain will opt out of, and the guarantees that will be secured against further integration. So far Mr Cameron has sensibly confined himself to generalities. Who can disagree with a call for Europe to be more competitive and open to the world and to interfere less in the nooks and crannies of national life? It is when the talk turns to special privileges and exemptions for Britain that things get tricky. The other day I heard a senior figure in Angela Merkel's government express palpable horror at the prospect of British departure. It would be a serious blow to Europe as well as to Britain. Ms Merkel, he continued, would do all she could to assuage concerns that eurozone integration could leave Britain marginalised in EU decision-making. Berlin could sign up also to an outward-looking, less intrusive EU. The German and other EU governments, however, have their own red lines. It is one thing to offer Britain assurances about the future, quite another to allow any member to opt out of parts of the union's acquis - the accumulated body of European law and agreements - that it finds inconvenient. To accept that approach would be to begin to unravel the entire enterprise. This points up the central contradiction that has doomed Mr Cameron's tactics from the outset. The Tory sceptics, now in a majority in the party, divide between those who want Britain simply to leave the EU and those who say they would consider staying in on radically different terms. These terms, however, challenge such basic tenets of the union as free movement of people, the jurisdiction of the European Court of Justice and the single market. They strike at the heart of the notion that the EU is a supranational institution. Britain's partners cannot but say No. There is a more than remote possibility, of course, that Mr Cameron will be unable to deliver on his pledge. Winning the next election will be more than a challenge. But decidedly ragged as the government now looks, Ed Miliband's Labour is scarcely a credible government-in-waiting. The opposition lead in the polls is soft and Mr Miliband could yet be panicked into matching the Tory referendum pledge. A Labour government would quite likely lose such a plebiscite. So there's the final rub. Mr Cameron could lose the election and bequeath, as a deferred legacy, Britain's flight from Europe. philip.stephens@ft.com*