Britain’s Europhiles could be forgiven for crying into their Carlsberg after the Danish referendum. Overnight, the Eurosceptics have transformed this small corner of Scandinavia into a matchbox version of Blighty and presented their campaign as a dry-run of our referendum. The Danish “Nej” is meant to be the end of our debate. But history may see it as the moment when the pro-Europeans finally came out fighting.
The reflex action of the yes camp has been to stress the differences between Britain and Denmark. The pint-size krone is indeed a less attractive target for speculators than an international currency like the pound. And as the krone was already pegged to the euro, it was difficult to persuade voters that the euro would bring any new economic benefits.

Denmark also has fewer floating voters. Public opinion has been hardened by six referendums on European questions in the past 20 years. This wearying succession of public debates has left few undecided. In Britain, there is still everything to fight for. Opinion polls show that almost half the country say they are “open to persuasion” on the euro.

The issues in Copenhagen were completely different. Many older voters feared that Denmark’s generous welfare state would be jeopardised by hard-nosed monetarists in the European Central Bank – not a common complaint here. And fears over Denmark’s power within the EU are similarly alien. The imposition of EU sanctions on Austria led to real public concern that small countries would be left powerless. Defeat in Denmark can teach pro-Europeans three important lessons.

First it shows that Blair must win the political – as well as the economic – argument on the euro. The Danish yes campaign showed beyond doubt that even the people convinced of the benefits for jobs and mortgages will still vote no if we lose the argument on sovereignty. The yes campaign should therefore argue that pooling sovereignty in the EU is the best way to maintain our influence over our everyday lives on economics, the environment and security. And outside the euro we will never punch our weight. This argument is already partly won. A majority of British public opinion is in favour of European action in the areas where they think it makes sense – on pollution and defence.

Making the political case for the euro will depend on getting the big picture right. The Danish yes campaign was defeated on the details. It often ended up on a defensive footing – frantically rebutting scare stories about pensions and tax harmonisation, because it failed to set out a practical, attractive vision of the EU. The prime minister needs to set out an EU blueprint to rival the federal super-state of popular imagination.

Timing is half the battle. The Danish campaign coincided with all-time lows in the value of the euro against the dollar and was called during a severe bout of mid-term blues. Tony Blair would be wise to keep his flexible formula on the timing of the referendum (“early in the next parliament”) if he is to avoid temporary storms blowing him off course.

There is often a temptation to preach to the converted. Of course it’s true that the public will listen to expert voices on economics and that views will filter down from the boardroom. But the yes campaign in Denmark spent a disproportionate amount of time and resources wooing the sharp suits that were already onboard. The next phase of the euro campaign in Britain has to take the battle from the business pages and CBI receptions to glossy magazines and kitchen tables.

The testosterone-fuelled political classes should not lose sight of the fact that the euro campaign will have to be targeted at women. A gaping gender gap proved fatal to the yes camp in Denmark, who couldn’t find a language and style to appeal to women voters. In Britain, according to a recent Mori poll, only 27% of women would vote in favour of a single currency compared to 35% of men.

The final lesson is the most important. Whatever the political strategy, Denmark has shown how the referendum will be won or lost by that most elusive of political commodities: public trust. This will be more important than the detail of economic argument and will have to come from politicians, not business leaders.

Though Danish business opinion was overwhelmingly in favour, the scepticism of a handful of high-profile bankers gave the impression that opinion was divided. As Bob Worcester convincingly argues in the Foreign Policy Centre pamphlet, How To Win The Euro Referendum, when expert opinion is split on complex issues, the electorate will respond to politicians they trust.

According to this law, Danish prime minister Poul Nyrup Rasmussen was doomed from the start. Ever since he failed to implement the “efterlon”, a manifesto pledge to lower the age of retirement, he lost public confidence. Only 8% of the electorate express “a lot of trust” in him. Even in the middle of the fuel crisis, Tony Blair scored much higher.

Preserving this trust means being obsessive about the credibility of your arguments. Don’t make claims for Europe that don’t stack up. Under the Tories, it was true that the EU offered people social protection that the government denied them. But everyone knows that they can get social benefits from a Labour government with or without EU support. This means focusing only on areas where Europe can add value: the single market, cheaper prices, environmental action, defence and the battle against organised crime. And it means being honest about the facts. The Danish yes camp was not believed when it made dark predictions of economic doom. British pro-Europeans should not flinch from pointing out the dangers of staying out of the euro zone, but they should steer clear of apocalyptic rhetoric.

Pulling off the greatest turnaround in public opinion since the war will be no easy task. The leader of the yes campaign in Britain will need to find a new political vocabulary, capable of reaching the parts that other politicians can’t. And they’ll need to do it at a time when faith in the political system has never been lower. But pro-Europeans should relish the challenge. We have all the arguments on our side. All we need to do is find effective proselytisers for our cause. To vulgarise a phrase from that fabled communicator in the Whitehouse: “It’s the politics, stupid.”

Mark Leonard is director of the Foreign Policy Centre.