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When David Cameron set about “detoxifying” the Tory brand, one of his first aims was to change the face of the party.

Painfully aware that he was surrounded in Parliament by (fellow) white middle-class men educated at public schools and Oxbridge, he sought to ensure that the next intake of Conservative MPs better reflected the country at large.

If he does become prime minister with even the slimmest of majorities, one thing is certain: he will have presided over the most radical single overhaul of the composition of the parliamentary party in history. Nearly 40 sitting Tory MPs are not seeking re-election — with a further trickle of last-minute retirements expected. Then there is the stark fact that the Conservatives must gain 117 seats to win an overall...