If Tory MP Douglas Carswell's defection to Ukip was grim enough for David Cameron, his decision to trigger a by-election (an admirable display of his democratic credentials) only heightens the danger. Cameron now faces the prospect of a Ukip candidate triumphing for the first time over the Conservatives in a parliamentary contest.
Carswell's strong personal brand means that he has been swiftly installed as the favourite. At the 2010 general election, he achieved a swing of 9.7 per cent from Labour to the Tories in his Clacton constituency (one of the highest in the UK) and won a majority of 12,068. As Anoosh noted, the seat is also the most demographically favourable to Ukip in the country. Should Carswell win, other Tory waverers may be emboldened to follow. This is a contest that the Conservatives cannot afford to lose.
The temptation will be to field a right-wing candidate with strong eurosceptic credentials (as in South Thanet, where they have selected a former Ukip leader to take on Farage), but it is one the Tories should resist. Rather, they should run a centrist figure capable of winning tactical votes from Labour and Lib Dem supporters. In the recent Newark by-election, a significant number of centre-left voters held their noses and voted Conservative on the grounds that it was the best means of stopping Ukip. One compared it to backing Jacques Chirac against Jean-Marie Le Pen in the 2002 French presidential election. Another said: "I've never voted Tory in my life, but I'm not having those bastards [Ukip] getting in".
Carswell's personal brand, as I said, is strong, and this thoughtful figure cannot be dismissed as a fruitcake, a loony, or a closet racist. But his new association with Ukip, a party toxic to many, will undoubtedly put some voters off. If the Tories are to hold the seat, their best hope lies in running a campaign that exploits that factor. As Carswell's defection has proved, you can't out-kip the kippers.