Oh dear Oh dear. Where to start. Mr Carswell.
1. He's undoubtedly right in believing that Cameron will flunk any reform negotiations - Dave has all the negotiating ability of a collapsed soufflé and about as much real commitment to fundamental reform as a nun writing a condom ad. Many Tories are exhibiting the triumph of hope over experience on this, convincing themselves that Dave will somehow behave completely differently to the way he has for the last ten years. There's no hope I'm afraid - he will flunk it, and be wholly humiliated, and will then flunk the Brexit referendum, leaving the UK as weak losers.
2. A minor but nonetheless niggling point - he's stolen Nigel's thunder as the first elected UKIP MP (or will do if he succeeds in the by election). While the gain to UKIP outweighs the stolen prize, it's a bit caddish.
3. Carswell is an unlikely hero. Committed to the privileges of the political class, he led moves to make the home addresses of MPs secret on election applications. Neither was his Localism book (with Dan Hannan) entirely original, owing much to both Simon Jenkins and Helena Kennedy, sometimes without attribution. If I met him in the pub, I wouldn't like him.
4. However, at least few care personally what happens to him. His move is useful in gaining UKIP air-time and in forcing Tory MPs to realise that Cameron's emollient charms are unsuited to the job in hand. It also brings back into discussion a Tory - UKIP election pact for 2015; if a worried party forces Cameron into this, Carswell's actions will be justified.