Conservative governments have a habit of self-destructing: they die not in battle with political enemies but as a result of vicious infighting. It’s been less than three years since Boris Johnson’s triumphant 80-seat election victory, which seemed at the time to come close to condemning Labour to oblivion. Yet this week in Birmingham it was the Conservatives who have looked doomed, posing a far greater threat to each other than to Keir Starmer.