By the end of this parliament, the UK may no longer be a member of the European Union – but this was little discussed during the general election. At no point in the campaign – with the exception of Tony Blair’s speech on the subject on 7 April – did the issue acquire the prominence that it deserved. Partly owing to the mistaken belief of many that Ed Miliband would become prime minister, the prospect of a Labour-SNP alliance attracted far more scrutiny. After the Tories’ victory, it is the European question that will now define British politics. The bill guaranteeing a referendum by the end of 2017 was supreme among those included in the first Conservative Queen’s Speech in 19 years. No piece of legislation in recent decades has been as potentially consequential.

David Cameron has embarked on the dual task of winning over his EU partners and his party, so as to create the conditions for a successful renegotiation and an In vote. To the distaste of some, he used the Riga summit on European relations with Russia to open discussions with his foreign counterparts. His announcement that EU migrants and under-18s – two groups likely to favour membership – would be barred from voting in the referendum was intended to reassure Tory MPs and Eurosceptic voters that the ballot would not be “rigged”.

Four decades ago, not long after winning a similarly slim majority (and defying the opinion polls), Harold Wilson announced that a referendum on Britain’s membership of the European Economic Community would be held within six months. These are far from the only parallels with today. Wilson, like Cameron, had initially resisted demands for a vote before relenting for the sake of Labour unity. As James Callaghan presciently observed in 1970, the policy was “a little rubber life raft into which the whole party may one day have to climb”. Rather than staging a referendum on the UK’s existing membership terms, Wilson also chose to pursue renegotiation. The concessions he secured, such as increased quotas for New Zealand butter and lamb (the country was a rival trade partner to Europe), were almost comically minimal. Yet the argument that the UK’s economic interests lay in continued membership (one championed by Margaret Thatcher, among others) trumped all else. The result was a decisive vote in favour of the status quo (67 per cent to 33 per cent).

Recent events have increased the confidence of the pro-EU side that history will repeat itself. The achievement of a Conservative majority has enhanced the authority of Cameron, who will be the de facto leader of the In campaign. Both his party and European partners are obliged to give him a fairer hearing than they anticipated. That the referendum is being held under a Tory prime minister is no small advantage for EU supporters. Under the “Nixon goes to China”principle, it is far easier for a Conservative Eurosceptic to win than it would be for a Labour Europhile. Cameron need not achieve all or even most of his aims, such as a four-year ban on welfare benefits for EU migrants and the exemption of the UK from “ever closer union” – merely enough to argue plausibly that a better deal is on offer.

As well as Cameron and other senior Tories, the pro-EU campaign will command the support of Labour (which has sensibly revoked its opposition to the referendum), the SNP (unlike in 1975), the Liberal Democrats, the Green Party, the CBI and the TUC. Their opponents will form a less eclectic coalition. Conservative MPs tell me that they expect up to a third of their number to campaign for withdrawal, among them current and former members of the cabinet such as Iain Duncan Smith, Chris Grayling and Owen Paterson. If Cameron is wise, he will again follow Wilson’s example and suspend collective ministerial responsibility, limiting the intensity of the split. Unfortunately for the Outers, those Tories poised to join them are hardly renowned for their public appeal.

This obstacle is modest compared to what Eurosceptics call “the Farage problem”. The Ukip leader is the country’s most visible proponent of EU withdrawal but he is incapable of winning over the moderates needed to deliver victory – and actively repels many of them. There is some polling evidence that Farage’s party has toxified the Eurosceptic brand as voters seek to avoid guilt by association. At the very moment that support for Ukip reached a record high last year, so did support for EU membership. Farage is a 15 per cent, not a 50 per cent politician. John Mills, the Eurosceptic Labour donor, who was national agent for the 1975 No campaign, told me: “You’ve got to have some kind of balance . . . to avoid it being polarised into Ukip against the rest of the country.” He suggested that Kate Hoey, the former Labour minister, should play a leading role. But there is no left-wing Eurosceptic of the stature of Tony Benn, Barbara Castle, Michael Foot or Peter Shore available. The death of the RMT general secretary Bob Crow last year deprived the Out campaign of another figure capable of reaching parts of the electorate that the Tories and Farage cannot.

The Eurosceptics’ great hope is that anti-establishment sentiment and discontent with the Conservatives will manifest itself through an Out vote. But the possibility of a referendum as early as next May reduces the risk of it functioning as a vehicle for midterm protest. Should economic growth collapse, the incentive to avoid further turbulence will only sharpen. History may yet record Cameron as the Prime Minister who presided over three referendums (on the Alternative Vote, Scottish independence and the EU) and preserved the status quo in each. For a Conservative leader, it would be an apt legacy.