“It’s cold outside” was the hardest-working slogan of the 1975 Euro referendum. For the Britons of the 1970s – recovering from fuel shortages and the three-day week – the story of a European future was more convincing than imperial nostalgia, the warm embrace of Washington or the charm of the Commonwealth. But what about this time round? The assumption of pro-Europeans has been that the sceptics will be a backward-facing rabble with little to say about the future. Are they right?

So far the Eurosceptics have told us much more about what they are against than what they are for. They attack the euro, austerity, the common agricultural policy, red tape, free movement. But once the referendum starts, the sceptics will need to reveal their own plans for Britain’s future. One of the biggest questions is whether the four main variants of Euroscepticism can coalesce into a single campaign – and whether the media will force them to develop a single alternative.

Of those four visions, “Singapore on steroids” is the most exotic account of our island future. Douglas Carswell – Ukip’s first member of parliament and the politician most closely associated with this vision – tells me that he is not sure if he ever used the phrase, and he is no fan of Singapore’s hereditary and authoritarian system of government. However, his vision of Britain as an outward-looking trading nation with a large financial sector, high levels of migration, a small state, low taxes and an internet-enabled democracy does resemble Asia’s most successful city-state in many regards.

Like Singapore, Britain would –according to this vision – have an active foreign policy, but it would try to extract economic opportunities from its relationships with others, rather than trying to shape the world. The state would shrink dramatically: government spending in Singapore is 14.5 % of GDP, compared with the United Kingdom’s 45%. It is less equal than any country in the developed world (even the United States) and nearly four in 10 of its population are immigrants.

Carswell is refreshingly blunt about the need for migrant labour: “Our grandparents’ generation had to get to grips with the idea of importing strawberries from Spain and mangetout from Kenya. Today we live in a world where labour mobility is inevitable, and unless you want to become like North Korea you need to accept it. You can no more ban labour mobility than food imports.”

Not so, claims the Ukip leader, Nigel Farage, whose vision is of a little England that restricts migration and withdraws from the common market to regain control of sovereignty. He appeals to the socially conservative instincts of people left behind by globalisation. At the last election, Ukip pledged to limit highly skilled work visas to 50,000 per annum – including those from the EU – while applying a moratorium on unskilled and low-skilled labour over the course of the parliament. Given the numbers of people who are leaving Britain every year, that would mean going from a growing population to one that shrank by hundreds of thousands of people a year. And a falling population would mean a downsized economy (Farage has said that “some things are more important than money”) and a downsized foreign policy. When I spoke to Farage he described Tony Blair’s messianic foreign policy as a post-imperial hang-up. Farage claims that no party in Britain has been more non-interventionist than Ukip: “Going into Afghanistan to make the streets of Britain safer is not something I ever saw the logic of … We couldn’t see the point of Libya. We don’t know what is going in Syria … We don’t want to get involved in any foreign wars.” Did Farage support any of the wars that Britain has been involved in since the second world war? “The Falklands, I’d have gone myself. And the first Gulf war.”

A third vision is of a leftish “People’s Republic of Britain”. Before he became leader of the Labour party, Jeremy Corbyn called the EU an organisation “that continues to pursue its central goal of being a place where big business has free rein to operate”. Since his leadership began he has tempered his Europhobia, but there is a persistent strand of leftish Euroscepticism that has been given added passion by the impact of austerity in the eurozone.

Kelvin Hopkins, one of a handful of Labour MPs who support withdrawal from Europe, claimed in the Morning Star that the EU was “a branch of global neoliberalism, of laissez-faire capitalism, constructed to raise up the power of the market and progressively dismantle the socialist and social democratic structures which were established and were so successful in the immediate post-war decades”.

Others on the left call for a populist campaign for a “Lexit” – a leftwing exit from the EU. At its heart would be a campaign to revive the ability of governments to implement the sort of industrial activism needed to protect domestic industries; opposition to the TTIP – the Transatlantic Trade Investment Partnership; and a programme of nationalisation of rail and postal services (though it is not clear to me that this would be illegal under existing EU rules).

There is a fourth vision of “out” that tries to look as much like “in” as possible – a model that can best be described as “bigger Switzerland”: no slashing of the state, no return of industrial planning, no closed borders. Its proponents claim that they would preserve the best elements of the EU while shedding the worst, and negotiate a magical set of treaties that enshrine this relationship. The choice is partly technical – what kind of trading arrangement do we want with the EU? What kind of border control?

There are two variants of this vision. Either Britain will try to keep access to the single market and negotiate a deal like Norway or Switzerland – a kind of EU minus. Both basically accept free movement (they have higher percentages of EU nationals living in them than does the UK), sign up to almost all EU law, and pay almost as much into the EU budget as the UK. They can theoretically choose not to apply EU regulations – though because they would lose access to the EU market in those areas, they have never actually done it. But they have big disadvantages: no voice in EU decision-making and no access to trade deals the EU strikes with the rest of the world.

The other model is Turkey, which has a customs union with the EU. Ankara neither benefits from nor offers free movement to the EU, and doesn’t need to apply all EU law. It doesn’t get access to the single market or EU global trade (though it is forced to open its market to everyone the EU strikes a deal with).

“The European project is inherently conservative,” says Carswell. Like other Eurosceptics, he casts Brussels as the ultimate blob, an alien force that subverts our democracy. But what the Eurosceptics do not acknowledge is that most of their ideas aren’t made impossible by the EU – but rather by the British electorate.

Today’s EU is as accommodating to free-market Slovakia with its flat tax and minimal state and Estonia with its internet-enabled democracy as it is to the flexible mixed economies of Scandinavia and the less flexible France, with its 57% of public spending and huge public sector. It would have little room for Farage’s utopia of no immigration or the left’s nostalgia for a closed managed economy.

However, it is not the EU that keeps Carswell from reducing the British state by two-thirds, or the radical left from nationalising the postal services – it is the British people, who have so far shown no great enthusiasm for these ideas. Hijacking the referendum and British scepticism about the union to promote these visions has been a clever move – but in reality the critics’ proposals have less to do with the EU than they make out.