I'm reluctant to write about this. The story is based on an anonymous source (or sources) who has viewed a military report that has not yet been released, and the report itself is only an interim report. If I get this wrong and rioting breaks out, I'll have to retract this post, and then my credibility, such as it is, will be in shambles. So with those caveats, which I recommend to all journalists everywhere...

On January 30, a Royal Air Force Hercules C130, a transport plane, went down in Iraq causing the greatest loss to British forces in any one incident. Speculation surged for a few days as to the cause, then was forgotten.

On Tuesday Thomas Harding of the Telegraph wrote that a cause has been determined—

An interim Ministry of Defence report has ruled out almost everything apart from enemy fire and it was suggested that a missile or rocket-propelled grenade could have brought down the aircraft.

But an official told The Daily Telegraph yesterday that the report concluded that the Hercules had been shot down by anti-aircraft artillery, as it flew at a low altitude, possibly 150ft.

"It was shredded by a multi-barrelled 20mm canon," the official said. "They have worked out that's what caused the crash."

The gun is believed to have been a 1960s twin-barrel Zu-23, made in China or the Soviet Union, left over from the Saddam Hussein regime.

It has an effective range of 2,000 yards and can be mounted on a lorry or set on wheels.

It is not known why the Hercules, which was equipped with sophisticated defensive measures, was flying at low altitude for the 40-minute trip.