Brian Sedgemore’s Insider’s Guide to Parliament has the irreverent flavour of the cartoon Beginners’ Guides whose presses its shares. His designation of Parliament as the House of Corruptibles demonstrates that he has sleaze in mind, and, heroically eschewing party political points, he rains barbs to right and left impartially.For one colleague only, Madam Speaker, his praise is unreserved.

Mr Sedgemore’s House of Corruptibles is a hall of mirrors, in which he is alternately guide and magician. His honest reflection first stares back at us, at pains to unravel the bizarre traditions of six centuries. It’s a cynical business, he seems to say, but this is how it works.

With homage to Machiavelli, he advises the aspiring politician: “Never outshine your patron”; “All politicians lie and Ministers lie the most;” “If you are an idealist, then politics is not for you”. In choosing a party the aspirant may also have an interest in such matters as why, if you believe the tabloids, Tory MPs get more sex than Labour MPs. Mr Sedgemore understandingly puts it down to Labour women believing politics is more important than sex, where Tory women are incapable of separating the two activities.

The aspirant should also be well briefed on the main theories of the right to lie. Here swiftly metamorphosing from guide to guard Mr Sedgemore sets corruption and deceit in public life flashing and glinting in repeated reflections. But which are true and which distorted by his mockery becomes impossible to say in this mirror world where lying in the national interest in laudable, officials merely give incomplete answers rather than peddle deceit, and a former Cabinet Secretary tells a meeting of the Inner Temple Historical Society that he was only economical with the truth once.

Brian Sedgemore is clearly himself without sin, to be able not just to cast the first stone with impunity, but to hurl such a continuous volley of brickbats. The only obvious charge against him, apart from outrageous name-dropping, is of making a quick buck for Christmas. He may even have had a skirmish with his conscience about the ethics of profiting in this way from others’ sleaze. But we need surely have no doubts that he will cheerfully declare the value of his royalties to the House.

For seriously, Mr Sedgemore is a mean moralist. Making everything a joke on the surface, further down he combines a Hobbesian realism with a Platonic concern for virtue in public life. While he ridicules the self-serving in close-up, his silhouetted shadow is ever beyond, juggling questions of truth and ethics.