On a programme on political diarists the other evening on Radio 4, it was remarked that in a century or so people will only know Cabinet ministers like Geoffrey Howe through the prism of Alan Clark’s diaries. The priapic fancier of Margaret Thatcher’s ankles might have been a smaller man politically, but history – through the longevity of his diaries – will judge him a greater man.

There are parallels, though slightly different, with Kublai Khan, a man whose name instantly evokes Coleridge and one of the most famous poems in the English language: 'In Xanadu did Kubla Khan/A stately pleasure-dome decree'. I bet those two lines