Like buses on a wet November night good books on Intelligence are rare – but to have three corkers like these arrive at once is a treat indeed. Intelligence is the hidden hand of history, often only revealing its real role years after the event, and this is certainly true of the trio of books under review.

The Black and Tans are so notorious – casting a shadow across Anglo-Irish relations to this day – that it is remarkable that Professor Leeson’s book is the first full academic study of them and also notable that Leeson is Canadian. Perhaps the lasting shame of the Tans’ rampages have inhibited British historians from tackling the topic.

The ‘Tans’ – so-called after a County Limerick pack of hounds, because of their mix of khaki and police blue uniforms – were actually two distinct bodies of recently demobbed Great War veterans: unemployed ex-soldiers recruited as special support for the depleted and embattled Royal Irish Constabulary; and a smaller unit of ex-officers, the Auxiliaries or ‘Auxies’, used as truck-borne raiding parties to hit back at the IRA flying columns that increasingly dominated the Irish countryside.

Recruited in desperation by Lloyd George’s Coalition in 1920 after Michael Collins’ IRA had wrested effective control of the country from Dublin Castle, the Tans’ deployment scarcely lasted a year, but was a PR disaster that sealed the fate of centuries of British rule in Ireland. Untrained, brutalised by the trenches and unfamiliar with the hostile terrain in which they operated, the Tans soon became a byword for savage over-reaction to the IRA’s own terror. Indiscriminate killings, burnings, torture and reprisals on innocent civilians turned the bulk of a previously indifferent population into fervent supporters of the IRA. It was a mistake that would characterise many other inept counter-insurgencies throughout the 20th century. Leeson’s study is perhaps a tad dry for the subject matter, but it lifts the lid on a discreditable episode of recent British history and paves the way for further research.

Light on another such discreditable episode is shed by Peter Day in Franco’s Friends, which, for the first time in book form, tells the full story of how Franco’s Spanish supporters in Britain, aided and abetted by MI6 agents, literally flew the future dictator to power. This was done by providing the little general with a pilot and a Dragon Rapide aircraft based at Croydon Airport (with two pretty blondes as cover) to get him from the Canary Islands to Spanish North Africa, where he took command of the rebel army as it rose against the Spanish Republic in July 1936 – touching off the Spanish Civil War.

The second part of Day’s book tells the perhaps even more important tale of how British agents – and British bribes of gold – kept Franco’s regime from joining his ideological ally Hitler in the Second World War – a precarious neutrality with untold consequences for the course of that war. This is an area, scarcely examined by British historians, which, like the Black and Tans, opens fruitful avenues for future research. Like Leeson, Day’s writing is rather dense and confusingly jumps around chronologically, but the research is impeccable and the subject matter fascinating – a real life Graham Greene thriller.

Snow is a remarkable tale of wartime double dealing, espionage and deception that has never been described in such detail before. Double agent Arthur Owens, code-named ‘Johnny’ by his employers in German military intelligence the Abwehr, and ‘Snow’ (an anagram of his name) by his British handlers, was an inventor and engineer and a fanatical Welsh nationalist. Loyalty to Britain held no appeal for him. He regarded the UK and Nazi Germany alike as big countries oppressing little ones – in his case, Wales. He was also embittered because he felt the British Government had cheated him out of money owed him for inventing an anti-Zeppelin shell in the First World War.

Owens was drawn into the sticky world of spying in the mid-1930s. He had invented a powerful electric battery extending the range of submarines, set up a company to market it and had no qualms about selling it to Hitler’s Germany. Owens journeyed frequently to Hamburg and Kiel to see his batteries installed in the new German U-boats. He was recruited by British Naval Intelligence to monitor the ports with an expert eye and report back: Owens was now a British spy. The problem was, he was also a German spy.

The duplicitous Welshman had offered his newly acquired spying skills to the Germans, promising to pass them British naval secrets. Unbeknown to Owens, though, the PO Box to which he posted reports to his German handlers, was being monitored by MI5. So British Intelligence knew from the start that he was double crossing them. For the next decade, across a Europe at peace and war, Owens and his spymasters in both countries played an extraordinary cat and mouse game in which it was difficult to tell who was Tom and who Jerry. This involved honeytraps with prostitutes, denunciations by Owens’ betrayed wife, turf wars between rival British intelligence agencies, trips to neutral cities in the midst of the war and Owens playing a starring role in the Double Cross system in which the Germans were fed duff information via radio sets and ‘turned’ agents in MI5’s hands. Owens was so distrusted by MI5 that he made his radio contacts to the Abwehr from inside a British prison cell.

Owens was finally taken out of circulation to the safety of Dartmoor prison. After the war he was given an intelligence pension – on condition that he kept his mouth shut and never set foot in Britain again. He never did, settling in Ireland, where he died in 1976, as near to his beloved Wales as he could get.

The experienced espionage writer Nigel West, with his access to MI5 files, has teamed up with a Welsh researcher Madoc Roberts to tell Owens’ story. It demonstrates convincingly the truth of the old adage that the world of espionage is a ‘wilderness of mirrors’, where no one is to be trusted and where final motivations and real loyalties often remain obscure. It is a jaw-dropping revelation of how unscrupulous and amoral men ignored the barriers of a world at war in pursuit of their own distinctly dubious ends.

Nigel Jones is the author of Tower: An Epic History of the Tower of London (Hutchinson, 2011).