More than 300,000 standard issue British Army rifles are set to be recalled after evidence showed the weapon was prone to jamming.

The Ministry of Defence faces a bill running into tens of millions of pounds for modifying the SA80 rifle.

Built by Royal Ordnance in the 1980s when it was under state ownership, the SA80 has been in use by the Army for more than a decade but there are serious concerns it jams in extremely hot and cold weather conditions.

Defence Secretary Geoffrey 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 whether to recall all or some of them.

He said: "As soon as I became aware I indicated, as a matter of some urgency, an upgrade programme should be considered and that is what is happening at the moment.

"I want to ensure that the rifle available is the best that is possible."

Mr Hoon said the cost was being looked at "very carefully" but added if they all needed replacing they would be, on a rolling programme so all soldiers would have rifles suitable to the conditions they were working in.

Click here to see the SA80's main problems

Fears had been raised from the start about its reliability in particularly hot, or extremely cold, conditions after soldiers reported the rifle could jam.

In campaigns in the Gulf and Kosovo, troops have used the weapon in the conditions most likely to render it unreliable.

Now, a study carried out by the MoD itself has revealed significant shortcomings.

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

The tests showed a modified version to be greatly improved.

More revelations

The news follows revelations earlier this week that £1bn modifications to the RAF's Tornado bomber had left it unable to drop modern laser-guided "smart" bombs.

Menzies Campbell, Liberal Democrat spokesman on defence, said: "This is the latest episode in the catalogue of embarrassment for the Ministry of Defence in relation to armaments and equipment.

"The SA80 was shown to be defective as long ago as the Gulf War, and again more recently in Kosovo.

"Isn't it time that someone took responsibility for these embarrassing and inadequate procurement projects?"

The Heckler and Koch report was given to Mr Hoon in December, and he is expected to announce a final decision on a recall within weeks.

BBC defence correspondent Jonathan Marcus said the implication of the defect was that lives have been put at risk although the MoD would probably discount such suggestions.

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