If Carswell was serious about Europe, he would never have defected

Where is this burning point of principle that drove Douglas Carswell into the arms of Ukip? I’ve read lots about his defection, and I’m still none the wiser. We’re told that he was talking to Farage for almost a year, which would have overlapped with the time he told me that the Tories need to unite behind Cameron because he was the only one promising an in-out referendum. What has changed?

Carswell says that Cameron is not serious about Europe. The Prime Minister has become the only leader in the continent to promise an in-out referendum. I’m not sure how much more serious one can be. Should he lay out, now, what he wants in a renegotiation? Of course not – it would be rendered rapidly out of date. The referendum would be three years away, and Europe is changing all the time. Back in January, Carswell told me that he understood this.