I must have watched The Great Escape two dozen times, so I'm familiar with the methodology of escaping from a prison.

I've watched Charles Bronson sweatily digging his way along, foot by foot, while Gordon Jackson and Richard Attenborough agitated a pathetic little fan to keep him breathing, and pulled sacks of dug-out earth back to the tunnel entrance on lengths of string.

So when, by contrast, I consider the details of the recent tunnel-break from Sarposa prison in the city of Kandahar, I cannot believe a word of it.

This is what they're claiming. Starting from a mud-walled compound, a gang of Taliban insurgents built a 1,050ft tunnel into the jail, so that it came up in one particular cell, where the ringleaders of the breakout were waiting. But who the hell, short of Nasa, has the direction-finding technology that can target a prison cell and steer a 1,000ft underground tunnel towards it with such micro-calibrated precision?

I'm well impressed. These guys should be making a fortune drilling for oil in the desert. But wait, there's more.

Somehow they got word about the tunnel to three Taliban prisoners, who later explained that they used their 'connections' to acquire copies of the cell keys. With the keys, the Taliban prisoners "managed to open doors for friends who were in other rooms". That's approximately 470 'friends' released from cells holding five or six each.

I've worked out that they'd have needed 94 keys to open so many cells.

I'd love a closer look at this super-tunnel, built over five months using the skill of several designers and down which 500 prisoners fled in a couple of hours.

Afghanistan's justice minister has advanced the theory that some prison guards might have been involved in the breakout. You don't say. I assumed from the start it was an inside job; the guards who heard nothing; the 'friends' who forged cell-door keys.

It seems obvious the Taliban and prison guards were as jointly culpable as Burke and Hare.

All they needed to do was smash a rough-looking hole in the floor of a cell and claim it was the end of a tunnel, without encouraging anyone to take a look inside.

It's just another example of Afghanistan's relaxed attitude to misbehaviour by its own people - however much Mr Karzai might wish to change them.

"This is a blow. It is something that shouldn't have happened," a shocked government spokesman, Waheed Omer, said.

"A prison break of this magnitude of course points to vulnerability . . . We have loopholes."

A loophole the size of a 1,000ft tunnel. A loophole that's a credibility gap the size of the Grand Canyon.