Born in Glasgow in 1912, Harrison was a classics teacher at Dornoch Academy at the outbreak of the Second World War. He was called up by the RAF but shot down on his first mission, bombing the Dutch port of Den Helder.
After being plucked from the sea by German sailors, Harrison settled into life as a prisoner of war. He moved from camp to camp, ending up at Stalag Luft III near the town of Sagan, now in Poland.
Harrison worked as a camp gardener and was introduced to Squadron Leader Roger Bushell, codename "Big X" (portrayed in The Great Escape by Richard Attenborough).
Bushell was the driving force behind the escape plot and his intentions were simple: "The only reason that God allowed us this extra ration of life is so we can make life hell for the Hun . Three bloody deep, bloody long tunnels will be dug - Tom, Dick, and Harry. One will succeed!"
Harrison acted as Bushell's runner and was tasked, as gardener, with dispensing the soil from the tunnels. The construction was laborious and involved 600 men. Two of the tunnels were discovered, but by March 1944, after almost a year, "Harry" was ready.
Only 200 participants were chosen to make the dash. On the night of the escape, Harrison, or Prisoner number 98, was waiting in hut 104, dressed in civilian clothing and armed with forged papers, when he heard gunfire. He promptly removed his escape clothing and burned the documents.
The gunfire was prisoner 77 being shot, and of the 76 who made it out into the tunnel, 73 were recaptured. Only three escaped successfully and of the 73, 50 were shot, including Bushell. Originally Hitler had ordered everyone involved to be shot, including the guards, security officer and camp architect; such was his rage at the escape attempt.
Years later, Harrison said: "The main purpose wasn't just to escape. It was to outfox the Germans. It was a huge moral victory. It humiliated Hitler and gave the Nazis a bloody nose."
It was that force of spirit and uncrushable honour for which Harrison and his comrades will be remembered most fondly.
Back in civilian life, Harrison resumed his teaching career at Glasgow Academy before moving his family to the Isle of Bute, where he became director of education. He retired 35 years ago, and took to long distance running in his seventies, before the years finally caught up with him.
His wife Jean predeceased him and for the last two-and-a-half years he lived at Erskine Home. He is survived by son Chris and daughter Jane.
This is an edited version of an article in `The Scotsman' on July 8.