By winning the economic argument, the Remain campaign believes it will win the EU referendum

To secure Brexit, the Leave campaign must overturn the most stubborn law in politics.

It was in 1992, the year the Maastricht Treaty was signed, that the strategy on which Britain’s EU membership now depends was distilled. “The economy, stupid”, read the sign hung by Bill Clinton’s campaign manager James Carville in his office in Little Rock, Arkansas. This insight has long since ossified into cliché. But few have prospered by betting against it.

Every recent presidential and general election has been won by the side most trusted with voters’ finances. The message that Brexit would depress growth and create economic instability has been – and will be – the Remain campaign’s weapon of choice.

On 15 April, the first official day of campaigning, the former chancellor Alistair Darling delivered a grim warning of the costs of withdrawal. Three days later, his Conservative successor, George Osborne, unveiled a Treasury document estimating the price of departure as £4,300 per household by 2030. Both men are reviving the tactics of recent triumphs. In 2014, Darling led the Scottish Better Together campaign, which mercilessly assailed its opponents’ Panglossian economics. In 2015, the Tories won the general election by casting Labour as irredeemably profligate (“Every day spent not talking about the economy is a day wasted” was the Conservative strategist Jim Messina’s echo of Carville).

Both campaigns were charged with insufficient passion and political monomania. But both won – the only measure by which posterity will judge them. So Remain has no intention of deviating from its strategy. The relentless labelling of it as “Project Fear” is testimony to its effectiveness. As one Conservative Brexiter, paraphrasing the former chancellor Norman Lamont, conceded: “It is hurting and it is working.” The Treasury’s 200-page assessment of the long-term cost of withdrawal will be followed by a second report on the short-term cost, including higher prices and job losses: “the really scary stuff”, according to a source.

In dismissing the Chancellor’s charges, the Brexiters only amplified them. Arron Banks, the millionaire Ukip donor and Leave.EU founder, described £4,300 per household as a “bargain basement price for the restoration of national independence”. The Remainers couldn’t have scripted a better response. Vote Leave, the official anti-EU campaign, avoided such recklessness but it struggled to rebut Osborne’s prognosis. Mainstream forecasters only differ on the extent to which Brexit would harm the UK economy – all accept the Chancellor’s essential premise. The Leave campaign has not produced what it truly needs to counter Osborne: a credible figure of estimated gains.

Michael Gove’s announcement that his side would reject continued membership of the single market offered greater clarity – but at the cost of inviting further economic obloquy. It was this unpalatable choice that led Dominic Cummings, the Vote Leave campaign director, to argue in a blog published last June: “There is much to be gained by swerving the whole issue. No 10 is dusting off its lines from the Scottish referendum.”

Mindful that it will not win on economic terrain, the Leave side has sought to shift the focus to immigration and sovereignty. It will appeal to voters to regain control of the UK’s borders and laws. Yet polling suggests that concerns of prosperity trump those of sovereignty. In a recent ComRes survey, 47 per cent named the economy as the definitive influence on their vote, compared with only 24 per cent for immigration.

The public may complain about being “run by Brussels” but for most the fear is abstract. At a recent Remain focus group, attendees were unable to name a single EU regulation that they would abolish. The best-known laws, such as paid holidays and parental leave, are also those that voters most wish to keep. The charge that Tory Brexiters long to repeal them is one that animates Labour supporters.

After what the Remain side concedes was a “difficult period” several weeks ago, the dissipation of the Panama Papers scandal, which diminished David Cameron’s credibility, and Jeremy Corbyn’s belated (and well-received) entry into the race have settled nerves. Remain leads by up to nine points in telephone surveys (which similarly favoured the Conservatives during the general election) and No 10 is confident that most of the undecided will break in Cameron’s favour.

Carville’s 1992 sign featured two further slogans: “Change v more of the same” and “Don’t forget health care”. Both give Leave hope. Remain strategists acknowledge the risk that the referendum becomes a catch-all protest against the status quo. Should the government’s ratings collapse, Cameron will be forced to remind voters, as he did during the Scottish referendum, that they are not passing judgement on him or the “effing Tories”. That he has announced his departure may prove an advantage.

The Leave side has sought to “weaponise” the NHS by proposing that the UK’s £8.5bn net EU contribution be redistributed in its favour – an offer that Remain concedes is having some success. Senior Labour figures and the Unison union will be deployed to ridicule the socialist credentials of Gove and Boris Johnson and to warn that economic turmoil would imperil the health service.

Labour, whose supporters constitute the bulk of the potential Remain vote, is no longer dangerously marginalised. Yet the Conservatives’ intensifying split continues to define the contest. The ferocity with which Osborne has targeted the Brexiters has led some Tory MPs to conclude that he has relinquished his leadership ambitions. But others believe that he is seeking a victory emphatic enough to allow Cameron to govern for several more years, giving him time to revive his diminished fortunes.

Before last year’s general election, Osborne declared that “water would have to start flowing uphill” for Labour to win. If Leave can yet triumph in similar circumstances, it will not just have defeated EU supporters – it will have defeated the most stubborn law in politics.