IT IS a mainstay of every election campaign when it looks as if the Conservative party will lose power. Some well-off celebrity will threaten to leave the country in the event of a Labour government. This time round, it is the charmless Katie Hopkins, a reality TV contestant turned columnist for The Sun newspaper. During the leader debates, she tweeted of Ed Miliband that “If this man is Prime Minister I will leave the UK. This man is not Great Britain. This is Russell Brand in a chuffing suit”. It is not clear whether Ms Hopkins thinks her declaration will cost Mr Miliband votes; some enterprising students have used it in a poster for the Labour cause. More than 200,000 people have signed a petition to have the columnist sacked, after she compared the migrants trying to cross the Mediterranean to cockroaches. History suggests that rash promises of permanent exile are rarely carried out. Before the 1997 election, several celebrities threatened to leave in the event of a Labour victory, including Paul Daniels, a magician, and Jim Davidson, a comic. Andrew Lloyd Webber, the composer, said he would leave if subject to "punitive taxation"; in the event, the Blair administration did not raise the top rate of tax. The only celebrity who seemed to carry out his promise was Phil Collins, the rock musician.

It takes quite a lot for people to leave the ties of family and friendship behind. And things are even harder for celebrities who may well be completely unknown outside the UK; Ms Hopkins is an unlikely recruit for Le Monde or The Washington Post. The very high levels of tax in the 1970s did cause a mini-exodus, including the Rolling Stones; the group produced one of their best albums, Exile on Main Street, while they were away. Sir Sean Connery, the former James Bond who is a noted enthusiast for Scottish independence, was another to leave; the Scottish Nationalist Party manifesto, with its proposals for a 50% tax rate and a mansion tax, seems unlikely to lure him back. (Labour has the same policy combination.)

A more serious threat would be if businesses decided to leave the UK in the event of a Labour victory. Again that is big shift. The introduction of the 50% top tax rate in 2010 (since cut back to 45%) caused a few hedge funds to leave the UK, But most stayed, amid talk of a "weekend wobble"; on Fridays they would be gung ho to leave, only to discover that their wives did not want to swap life in London for the more staid delights of Zug or Geneva. By Mondays, the threat would be forgotten.

This time round, only Michael Spencer, the noted Tory donor and head of the ICAP money broker, has raised the issue. Set against that threat is the possibility that other employers will leave the country if the Conservatives win and David Cameron's pledge to hold a referendum on European Union membership in 2017 goes wrong; multinationals may value the UK as an English-speaking hub within the EU. Losing a car manufacturer would matter a lot more than a columnist.