If Benito Mussolini had sustained Italy’s neutrality in the second world war, instead of jumping aboard Hitler’s bandwagon in June 1940 in anticipation of sharing the pillage of Europe, he could have profited mightily. It is unlikely that the Nazis would have invaded his country. The victorious allies would have heaped rewards on Italy, fascist or no, for staying out. “Musso” might have continued to tyrannise his own country to a ripe old age.

This was indeed the experience of his fellow dictator General Francisco Franco, a monster with more blood on his hands than Mussolini. The Spaniard persisted with the wholesale murder of his defeated civil-war enemies all through the second world war, and indeed afterwards. He sustained his tyranny until dying in his bed in 1975.

To this day, imbecile right-wing pundits – some of them British – pay homage to Franco’s statesmanship and the “sound” governance of his country. In truth, as Stanley Payne’s book emphasises, Spain’s abstention from the second world war was the product of clumsy diplomacy rather than of wisdom.

Franco fully intended to join the axis struggle against the democracies. It often goes unnoticed that Spain’s wartime status was not that of a true neutral nation such as Switzerland or Sweden, but of nonbelligerence, which Payne suggests could more aptly have been described as prebelligerence.

On October 23, 1940, Spain’s leader had his one and only personal meeting with Hitler, at Hendaye on the border with France. The Caudillo arrived late not, as his admirers claimed, in a clever piece of one-upmanship, but because of the inadequacies of the Spanish rail system.

Hitler imagined that the encounter was a formality, at which Franco would merely announce the date of his entry into the war. Instead, to the Germans’ dismay, the Spanish leader produced a long shopping list of conditions for participation, new colonies in Africa prominent among them.

Hitler wished to send German troops into Spain to seize Gibraltar. Franco perceived such a proposal as an insult to his own army. He was anyway uneasy about inviting panzer grenadiers to camp on his doorstep. He told the disbelieving Germans that his own troops could take care of Gibraltar, once they had been reequipped with the German weapons and planes he needed. Hitler was exasperated not only by Franco’s presumption, but by the garrulous Spaniard’s long monologues and personal reminiscences, which the Führer perceived as his own prerogative.

By a bizarre twist, the most significant deal-breaker was Spain’s claim to a chunk of Vichy France’s African empire. The Hendaye meeting came weeks after Vichy French forces at Dakar had repulsed a British and Gaullist attempt to seize the port. Hitler cherished hopes that this action presaged active Vichy military support for his armies. Dakar, which was at the time perceived in London as an unalloyed fiasco, thus yielded an uncomprehended blessing: Hitler refused to offer Franco French colonial possessions in return for joining the war.

Thus passed what subsequently proved a turning point. Though Franco continued to dicker with belligerence, and maintained his faith in axis victory until at least the end of 1942, the moments at which the Spanish were willing to fight never coincided with those at which the Germans thought their price for doing so worth paying.

The story of Spanish dealings with the Nazis represents a fascinating marginal entry in the history of the second world war. The duplicity, cynicism and sheer nastiness of Madrid’s rulers invites awe. The British paid millions in bribes to Spanish generals to stay out of the war, but there is no evidence that these influenced their behaviour one way or the other.

Payne mentions the famous 1943 deception operation Mincemeat, when the British planted on the Spanish coast a corpse, supposedly that of an officer carrying secret papers foretelling a landing in Sardinia. The British correctly anticipated that the Spanish authorities would immediately pass the forged documents to the Nazis.

It is highly debatable, however, whether Payne is correct in supposing that the ruse caused German forces to be diverted from Sicily. Like so many splendid buccaneering operations of the second world war, “The Man Who Never Was” provided much pleasure for his creators and postwar movie audiences. But there is no evidence that it changed history.

Times Recommends

• The Sunday Times 100 best holiday reads
• What will we be reading this summer: the booksellers predict
• Literary festivals: a survivor’s guide