Cameron must now show his mettle and take proper advantage of Labour weakness

This is turning into a summer of extraordinary good luck for the Conservatives. First the Norwich North by-election victory, then the extraordinary success of the Totnes open primary. And all set against the background of what is, for Tories, the most mellifluous sound in politics: Harriet Harman’s voice. As David Cameron enjoys what will probably be his last real holiday for several years, he has a comfortable dilemma: now all this good fortune has arrived, what will he do with it?

A basic formula has governed British politics in the last 35 years: the more useless Labour becomes, the bolder the Conservatives can be. Mr Cameron is at his most active when facing disaster, as he demonstrated with radical welfare and education policies ahead of the election-that-never-was in 2007. But success seems to paralyse him, as if he is afraid any movement will break the charm. Given how murderous his job would be as Prime Minister, he cannot afford to let any opportunity for radicalism pass.