The four tunnels were given nicknames - Tom, Dick, Harry and George - by the POW escape committees. One of the most important finds, a home-made radio, was unearthed in the George tunnel.
An attempt last August to re-excavate Harry, the route for the main escape effort, was abandoned when it became apparent it could collapse. There was also a suggestion that the Nazis, who immediately filled the tunnel when it was discovered, had packed it with explosives.
Other objects found included ventilation pipes made from tin cans and part of the "railway" track used by the prisoners to travel along the tunnels as they dug.
Channel 4's team also recreated many of the ingenious devices and processes used in the escape. These included making compasses from gramophone styluses and treading tonnes of sand from the tunnels into the earth around the camp - all under the noses of German guards.
Several surviving World War II airmen joined the project. Air Commodore Charles Clarke, 88, from 619 Squadron, said: "I've been back a number of times, but it's always emotional. We had doubts in our own mind as to whether it was right to open the tunnels up."
Despite The Great Escape, starring Steve McQueen, taking many liberties with the truth, Clarke is full of admiration for it. "People often ask me about it. Of course, there weren't as many peaked caps and not as much saluting, and obviously the motorcyclist [McQueen's famous fence-jumping stunt] wasn't there. But, without the film, who would remember the 50 who were murdered?"
- INDEPENDENT