When Malcolm Muggeridge was working for MI6 in newly liberated Paris, he witnessed a scene that sheds light on espionage in general and the subject of this book in particular. After a bibulous dinner, his boss, Kim Philby, head of the department dealing with Soviet counter-intelligence, suggested that they should walk to the Rue de Grenelle. There Philby shouted and gesticulated at the fortress-like Russian embassy in an almost demented fashion.

Muggeridge was baffled. But after Philby's defection he concluded that in playing the double-agent game "the magnetic field of one's mind gets dispersed, with the particles flying here, there and everywhere. Instead of straining after an integral self, one becomes first two, then maybe several other selves, functioning independently." It was like living a novel, playing each character by turns and changing allegiance as the plot developed.

James Hayward doesn't mention Muggeridge's aperçu in this account of the career of Arthur Owens, billed as Hitler's chief spy in England and code-named Snow. But his book certainly reads like a novel  rather a trashy one. And about the only thing to emerge from it with crystal clarity is that nobody knew where Owens's real loyalties lay, perhaps not even himself. John Masterman, the Oxford don who became chairman of the Twenty Committee (XX signifying double cross), which ran double agents in Britain, said that the riddle of the Sphinx and the doctrine of the Trinity were straightforward matters compared with distilling truth from Snow. Hayward, while acknowledging that Owens's prime motive was greed, seems to think that he was a Nazi at heart. Yet thanks initially to him, Masterman came to control the entire German espionage network in Britain.

Arthur Graham Owens was born in Wales in 1899. After studying science he became a "manufacturing chemist" and would-be inventor. One of his earliest inventions was a story that his father's engineering firm had devised a special shell that shot down flocks of Zeppelins, for which the War Office refused to pay. He married a woman called Irene Ferrett and quickly frittered away his inheritance on a failed confectioner's shop in Mumbles  Hayward, in one of his better jokes, calls him a humbug merchant. Owens emigrated to Canada but returned home during the depression to exploit patents he had registered in new battery technology. He made frequent business trips to Germany and in 1936 British security services began to use him as a freelance agent. Soon afterwards Owens was recruited by the Abwehr, which paid much better.

He was anything but an attractive asset, resembling not so much James Bond as Mr Verloc, Conrad's seedy secret agent. Owens was short, slight and unkempt, with a thin, shifty-looking face and bony, nicotine-stained hands. One Special Branch officer described him as a typical Cardiff type with the general "appearance of an underfed rat". Owens appalled his British handlers by putting in his false teeth at meal-times, and disgusted his German controller, Captain Nikolaus Ritter, by concealing microfilm under the plate in his mouth. Furthermore Owens was wildly spendthrift and vaingloriously indiscreet. He drank a bottle of whisky a day and was serially unfaithful to his wife, who left after accusing him of treachery to both MI5 and the Abwehr.

Hayward says that no one on the British side seriously considered that Owens might be working for the Germans, and it is true that at one point his case officer, TA Robertson, deemed him "entirely trustworthy". Yet, on Hayward's own showing, MI5 remained viscerally suspicious as Owens continued to meet Ritter and supply him with information about ports, airfields, munitions and troop movements. Most of this was low-grade stuff, tolerated by Robertson because it helped to convince the Abwehr of Snow's bona fides, though he also made unauthorised disclosures, notably about the importance of radar. But when the war broke out MI5 watched Owens ever more closely, bugging his house, surrounding him with stool pigeons and directing his radio transmissions.

These often sounded like propaganda bulletins, particularly the warnings about Churchill's preparations to repel a German invasion. Snow even reported that the British had acquired 200 man-eating sharks from Australia for release into the Channel. Luckily the Abwehr was equally amateurish. It parachuted in agents equipped with obviously forged papers as well as chunks of German sausage and torches stamped "Made in Bohemia". Some spies were executed while others were "broken" and "turned". They became part of the double-cross system whose crucial achievement was to help convince Hitler that the D-Day landings would take place on the Pas-de-Calais.

Meanwhile Owens had pursued his picaresque trajectory. Among its racier episodes were his abortive rendezvous with the Abwehr on a North Sea trawler, which culminated in Snow's being tied up and returned to Grimsby; his trip to meet Ritter in Lisbon, from which he brought back nothing more substantial than a dose of clap; his incessant interrogations by MI5, which finally prompted Masterman to take him to Harley Street to find out if he was mad; and his eventual imprisonment in Dartmoor. Owens was released towards the end of the war, after which MI5 paid him £500 to disappear. He died in Wexford in 1957 and was buried in an unmarked grave.

Hayward's narrative rattles along briskly, but it is marred by a relentless facetiousness. For example, he peppers the text with one-paragraph comments expressed in the transatlantic slang favoured by Owens: "humdinger"; "right hot"; "absolute jake". The book adds little to a previous work on Snow, produced only last year by Nigel West and Madoc Roberts. And it is impossible to check on the sources, themselves tainted, since the references have been consigned to a website that does not seem to exist. Finally, Hayward fails to set his story in its proper context: the looking-glass world of secrecy and deceit, which has always exerted such an attraction on crooks, drunks, frauds, fantasists, adventurers and traitors.

 Piers Brendon's Eminent Elizabethans is published by Cape.