Simon Cowell isn’t known for his diplomacy on screen – but it was the Britain’s Got Talent judge’s early days on X Factor when his most venomous criticism came out.

Once, he sharpened his claws in preparation to tell a contestant from Eastern Europe: “I don’t know what cats being squashed sound like in Lithuania, but I now have a pretty good idea.” To another contestant, he raised the idea of a pre-medieval era punishment, exclaiming: “If you had lived 2,000 years ago and sung like that, I…