The cost of modifying about 300,000 faulty army rifle - which is likely to run into millions of pounds - is expected to fall on the taxpayer.

All SA80 rifles are set to be recalled after evidence showed the were liable to jam in extreme temperatures.

And because the weapon was designed by Royal Ordnance - when it was state-owned - the repair bill is now expected to be footed by the Minstry of Defence.

Government officials have not put an estimate on the final cost but it is widely expected to reach tens of millions of pounds.

The SA80 disclosure follows a similar embarrassment earlier this week, when it emerged that Tornado GR4 jets were unable to drop precision bombs.

Defence Secretary Geoff Hoon denied British forces were working with "lousy equipment", as he insisted the latest problem could be solved.

Mr Hoon told the BBC he had commissioned a report into possible upgrades as soon as he was made aware of the jamming problem.

But he said he would wait for the report's conclusions before deciding what action to take.

He also made it clear that if the weapons were recalled it would be on a "rolling" basis rather than all at once.

Click here to see the SA80's main problems

The Royal Ordnance SA80 was introduced in 1986 to replace the ageing Self-Loading Rifle, which had been in service since the early 1960s.

The main rival for the contract was the US M16 rifle, which is the preferred weapon of special forces such as the SAS and the Special Boat Squadron

Difficulties with the SA80 were first reported in the 1991 Gulf War, where British troops fought in the desert heat, but it was not until 1995 that the concerns were confirmed by tests.

In 1998, arms manufacturer Heckler & Koch was asked to modify the weapon and carry out extreme temperature tests in Kuwait and Alaska.

The tests showed the modified version to be a great improvement on the original.

But shadow defence secretary Iain Duncan Smith said Labour had been "dragging their heels" over proposals to modify the gun.

"It has taken them two years to finally admit there are problems with this weapon, despite many soldiers voicing their great concerns over the rifle throughout this period," he said.

Menzies Campbell, Liberal Democrat spokesman on defence, said: "The SA80 was shown to be defective as long ago as the Gulf War, and again more recently in Kosovo.

"It is extraordinary to me that the weapon wasn't subject to the sort of rigorous testing in advance that would have indicated how good it was in severe conditions."

History of problems

The Labour government is not the first to face problems with the SA80.

Labour's Bruce George, chairman of the Commons Defence Select Committee, said he had followed the "sorry saga" of the rifle since the early 1980s when the Conservatives were in power.

But he insisted it was difficult to pin blame on anyone.

Mr George said his committee would now ask for a copy of the latest report and investigate whether the government was taking the right action.

He said the government's weapons procurement programme meant that problems with armaments would be greatly reduced in future.