Thousands of SA 80s are in use as the personal standard issue weapon for the Army, Royal Navy, Royal Marines and RAF.

But since its introduction in 1986 soldiers have been dissatisfied with it.

'Mostly works'

Now the MoD has admitted "work is under way to identify problems" with the weapon, which was manufactured by Royal Ordnance.

A spokesman refused to say what the problem with the weapon was, but it is believed it may jam under severe conditions.

"It is the case that there are problems in the most extreme hot and dry conditions," said the spokesman.

But he was keen to play the problem down, stressing "in most conditions" the rifle works well.

The spokesman said a programme of improvements to the rifle would be introduced, but he could give no indication when that would happen.

'Jams in the desert'

Lord Gilbert, the defence procurement minister, wrote to the defence committee about the problem last year. The letter was published on Wednesday as part of the committee's annual report.

The letter said the results of trials dating back to 1995 had shown there could be underlying reliability problems.

The Special Air Service and the Special Boat Service do not use the SA80, preferring instead to opt for American weapons.

More than 330,000 of the rifles have been bought by the Ministry of Defence at a cost of �384m.