Prime Minister David Cameron was facing a severely destabilising by-election last night after a Tory MP sent shockwaves through Westminster by defecting to UKIP.
Eurosceptic backbencher Douglas Carswell stunned the Conservatives by quitting the party and heavily criticising its leadership.
The fall-out from the defection – which represented a significant coup for Nigel Farage’s UKIP – caused Mr Cameron a major headache as he arrived in Glasgow to deliver a speech on the perils of Scottish independence.
The announcement was seized upon by the SNP last night, with Angus Robertson branding it “another step by Westminster towards the European exit door”.
Mr Carswell delivered his bombshell at a hastily-arranged press conference, accusing Mr Cameron of being “insincere” and not “serious about real change”.
His decision to resign and seek a mandate to represent his Clacton constituency in Essex for UKIP has paved the way for a by-election that is sure to re-open old divisions in the Conservatives about Europe.
The timing of the row could hardly have been worse for the prime minister, with Tory strategists already concerned about losing vital votes to UKIP in May’s general election, but also with Scotland’s independence referendum just three weeks away.
Reacting to the news while in Glasgow, Mr Cameron said: “It’s obviously deeply regrettable when things happen like this, when people behave in this way.
“But it’s also, in my view, counterproductive. If you want a referendum on Britain’s future in the EU – whether we should stay or go – the only way to get that is to have a Conservative government after the next election.”
Sitting alongside Mr Farage at a press conference in London, Mr Carswell said the failure to take a stand against the European Union was at the heart of his decision, among other concerns.
“They are not serious about real change. It’s above all the failure to deliver on the promise of political reform that has driven me to be here today,” he said.
Mr Farage hailed the defection as the “bravest, most honourable and noblest” he had witnessed in British politics, describing him as a “perfect fit”.
Labour leader Ed Miliband said: “Douglas Carswell’s defection is not just a blow to David Cameron. It shows the Tory Party is too divided to stand up for hard-working families.”
Mr Robertson, Moray MP and SNP Westminster leader, said: “This marks yet another step by Westminster towards the European exit door.”