Stop the world. Britain wants to jump off. The 2012 Olympics were a glorious celebration of diversity. London presented itself as an unrivalled global hub. The local heroes of the games – athletes such as Mo Farah and Jessica Ennis – testified to a new, expansive view of Britishness. That was then.

A year on, the nation’s politics echo to the sound of doors slamming shut. The message to foreigners is depressingly simple: stay away. David Cameron’s Conservatives promise a referendum that could lead to Britain breaking off engagement with Europe. There was a time when these Tory sceptics presented a choice: give up Europe and look to the world. No longer. The barricades are being thrown up against all and sundry. Tourists, students, business executives – all are would-be illegal immigrants.

The message? Illegal immigrants should “go home or face arrest”

The other day, the Home Office, the department responsible for border controls, gave a glimpse of the nasty populism driving government policy. Trucks with billboards were deployed to London’s ethnically diverse areas. The message? Illegal immigrants should “go home or face arrest”. The Liberal Democrats, the junior party in Mr Cameron’s coalition, protested that the initiative was stupid and offensive. Unmoved, the prime minister’s office said the campaign might well go nationwide.

The Home Office also plans to require visitors from “high risk” countries to pay a £3,000 cash bond to enter Britain. The aim, so it says, is to deter “overstaying” and to recover costs if visitors require healthcare. The countries chosen are India, Nigeria, Kenya, Pakistan, Sri Lanka and Bangladesh. It has not escaped their attention that predominantly “white” nations such as the US, Canada, Australia and New Zealand are exempt.

Closer to home, the government is promising to restrict the access of Romanians and Bulgarians. Nationals from these EU states gain free movement across the union when transitional restrictions expire next year. Britain’s tabloid press is already full of horror stories about hordes of “benefit tourists”. Never mind that migrants are less likely to claim welfare than Brits.