Real World War Two hero and Trinity graduate Sir Tommy Macpherson talks to John Garth about how he used his wits – and kilt – to bamboozle the Nazis.

For many of Oxford's Michaelmas intake of 1945, real life had already arrived with hurricane strength in the war years. Among these military veterans, few can have known life as fully as Tommy Macpherson. He had already seen battle, been a prisoner-of-war and serial escapee, terrorised the Germans as a special ops commando leader in France and Italy, helped establish the Cold War boundaries of Western Europe, and received the first of a plethora of ribbons and medals. Until last October, when it was published as Behind Enemy Lines: The Autobiography of Britain's Most Decorated Living War Hero, his full story was known only to his family. It's the very stuff of stirring war films, crammed with more incident than could fill at least two trilogies of action-packed epics – and the putative film director would need to be able to handle abrupt shifts of tone. At one extreme, there are set pieces worthy of Where Eagles Dare, with dark, violent vignettes of torture among rival partisans. At the other, there are moments more reminiscent of 'Allo 'Allo!, such as when a drunken RAF pilot, fancying a nap mid-flight over Italy, hands the controls to the wholly non-aeronautical Macpherson. And some of Macpherson's greatest achievements encompass both comedy and high drama: a consummate confidence trickster, he once won the surrender of 23,000 Wehrmacht troops with nothing but a sidearm, a swagger and a few brazen lies.

At 90, Sir Tommy Macpherson regularly visits Oxford as president of the Achilles Club, the organisation of Oxford and Cambridge athletes who have competed in the annual Varsity Match. He and his wife Jean divide their time between homes in London and Newtonmore, Invernessshire, where he grew up; they have raised two sons and a daughter. He was born in Edinburgh in 1920, the youngest, smallest and sickliest of seven siblings – he suffered streptococcal diphtheria and osteomyelitis – but he was determined to outdo his elder brothers, including George Macpherson, one of Scotland's rugby greats.

He recalls: "I wanted to compete all the time. Because I was not well, I had to be better than them. I had to bat on."

He was due to go up to Trinity in 1939 but that Easter, as Britain belatedly armed itself against Nazi Germany, he won a commission in the Queen's Own Cameron Highlanders, a Territorial Army unit. The Somme and Ypres seemed to define what war would be: "We all expected to be dead anyway." But his youth enabled him to look on this with equanimity – "I was only a boy. Nothing was normal and you just go ahead." Still fresh were the habits of discipline learned at Fettes, where he had been a sergeant in the Officer Training Corps. "For my brothers, it was much more difficult because they were much older and they were into their careers." He trained with the TA, but when the Special Operations Executive was formed on Churchill's orders in July 1940 with a mission "to set Europe ablaze", Macpherson volunteered for one of its first units, No 11 Scottish Commando. His own war could not have been less like the tragically static trench experience of 1914–18. "In the Second War, at the beginning nothing happened; then suddenly, later, things happened very quickly: you would really be all over the place," explains Macpherson.

His first taste of combat was on 9 June 1941, when the commandos led the crossing of the Litani River in southern Lebanon. He recalls the shock, but also the mixture of adrenaline and responsibility that took the edge off fear. "You were changed immediately," he says. "You are very important because of all the other boys; and you've got to tell them, 'Yes, come on boys! Come on!' – and that was good because you weren't all that scared for yourself. Alright, they were probably scared, but we had to pretend as if we were not." At another point, talking of his aforementioned surprise stint as a stand-in pilot, Sir Tommy denies feeling any fear at all. Yet when asked whether he felt fear at any point during the war, he unhesitatingly states: "Yes, all the time." The contradiction perhaps resolves itself in terms of the classic observation that genuine courage is not the absence of fear but victory over it.

Macpherson's next operation was an ignominious flop: scouting the Libyan coast in November 1941 with three other men in folding canvas boats. The submarine that dropped them off failed to pick them up again and he was captured by Italian carabinieri. The first of many escape attempts followed almost immediately. His captors blithely handed his Colt revolver back to him so he could show them its workings, but they had overlooked the spare cartridge he had in his pocket. He slipped it into place and held them at gunpoint. "It was very simple and they were very stupid; but as I got away, suddenly I couldn't move" – an attack of cramp consigned him to two years as a POW in Italy, Austria, Germany and Poland.

He never quite despaired of escaping. "Every now and then you would think, 'Oh God, this can't go on.' Then something would happen and you would understand that yes, you were going to get a chance again." The privations of the fortress-prison of Gavi near Genoa were grim. "There was not enough to eat and it was very cold," he remembers. "It was really very difficult." Coming from someone who could apparently face down a dozen deadly perils before breakfast, the word "difficult" acquires peculiar force. But he turned incarceration there to his advantage by learning fluent Italian. Macpherson finally achieved freedom in Poland in 1943 by disguising himself as a worker, catching a train to Danzig and burying himself in coal on a Swedish ship. On the train, he inadvertently sat beside an SS officer, whose intimidating presence left the guards quite uninterested in checking Macpherson's ticket or papers.

Arriving home, he expected to be shuffled away behind a War Office desk, but his experience behind enemy lines plus his excellent spoken French (learned at Fettes) made him an ideal candidate for Operation Jedburgh, a role that defined the rest of his war. Three-strong commando units were to drop into France and harry the occupiers to stir up French courage. Macpherson parachuted into the Massif Central two days after D-Day, and discovered the maquis there were virtually non-existent. "When we went out we were told that lots of people would be there for us, but we got there and there were almost no partisans," Macpherson explains. But he and his small band blew up a bridge the night after he landed, and continued to destroy bridges, pylons and railway tracks virtually every night thereafter.

His greatest assets were daring, quick thinking, and a car to facilitate hit-and-run strikes. His special delight was in arranging the charges to bring pylons crashing down against each other with full fireworks. "There was no difficulty, nobody else shooting at us, we were soon way away and so that was just fun." He blocked a German convoy by blasting trees against each other and booby-trapping each pair in a different way to cause maximum delay and casualties. Such bravura performances went far beyond his training. "At the back of it, you know all the things you've learned, exactly by rote," he says. "But then one had sudden unplanned details to deal with and things changing quickly. We had to do things very quickly but be very careful. You would leave and it was done, and then there was the next one to do." Did he never panic? "Oh, for goodness sake, no. It's vital to see, to attack, to do it there, quick; because if you're too slow, you're dead. One mistake's enough."

Having access to a car made Macpherson ubiquitous but perpetually elusive. To undermine Nazi authority, and thereby swell partisan numbers, he drove about in his Cameron Highlander tartans, openly flying the Union Flag pennant and the Croix de Lorraine from his black Citroën. Did any of those he worked with tell him, 'No, this is stupid, you'll get shot'? Yes, he laughs – all the time. He ignored the price on his head (300,000 francs); the partisans grew in numbers and confidence. His chutzpah reached its apogee when he decided to stop 23,000 retreating Wehrmacht troops from high-tailing it to Germany ahead of the advancing Allies. He presented himself, in his tartans, to the commanding officer and told him that heavy artillery, 20,000 troops and the massed RAF were all waiting for his word to attack the column. It was total moonshine, but the German general swallowed it whole and surrendered.

The Italian episode of 1944–5 was darker and harsher. Rough terrain and wintry conditions ruled out cars, so Macpherson had to keep a low profile. It soon became clear that the Communist partisans had their own agenda and he had to abandon his headquarters after they put a price on his head. "I thought I'd done quite well there, but after four months they had changed completely and we were against them from then." When the Communists raided the old HQ, they tortured and murdered two Italian partisans faithful to Macpherson. Finally, during the German retreat, he had to forestall any further Nazi atrocities and simultaneously thwart a Communist bid to seize the entire province of Veneto for Tito's Yugoslavia. He sent loyal partisans to guard important Catholic clergy and deployed snipers to keep the Germans busy. Calling the Nazis' bluff once again, he took the surrender of a garrison – with the help of his kilt. When the Allies arrived, his local knowledge enabled them to pinpoint and quash the Communist insurgency. Though he has earned an array of medals that would make the most puffed-up dictator blush – among them a Croix de Guerre, three Military Crosses, a papal knighthood and the order of Chevalier of the Légion d'Honneur – the borders of north-eastern Italy are surely the best tribute to Macpherson's courage and ingenuity.

Yet he is at a loss to name his proudest moment. "You know," he ponders, "it's very often that one remembers the small things and forgets the big ones." As for regrets, he is pained to recall having to stand by while, in the exigencies of war, his partisan associates shot their own compatriots. His own kills included a German officer decapitated by a level-crossing and a soldier in Italy stabbed in close combat after shooting Macpherson (the bullet was deflected by his backpack webbing and his notebook). There was no time for sensitivities: "It's either you or them. You can't change what's done." The war ended just before he could be redeployed in the Far East. Though it dominates his autobiography, he sees his war as a remote chapter of his life. "To me it was dead long ago, and the rest of my life has been much longer – and rather good."

Two weeks after his return from Italy he started at Trinity. He took PPE – not because of any innate philosophical tendencies but because it would give him the most time for rugby, hockey and running. But he enjoyed economics – which proved an asset in his business career in timber – and he jousted feistily with his tutorial partner, Tony Crosland, later a Labour cabinet minister under Harold Wilson. Macpherson credits Oxford with easing him and his fellow servicemen back into civilian life. "We were extremely lucky," he says. "Our life was finished, and then it started again." The companionship of fellow veterans counteracted the bathos of his abrupt move from commando leader extraordinaire to undergraduate. He mixed little with the undergraduates who were fresh from school, except on the athletics track, where he excelled. A wartime camaraderie persisted among the veterans and for Macpherson so did the journeys into Europe as his rugby team went on tour. He says he could not have gone straight into a career: "I couldn't have coped. It was wonderful to have that." Despite completing his course in two high-octane years, he achieved a First: "Oxford seemed to go extraordinarily quickly, and then we were in the world."