A group of soldiers approached The Times in Kuwait and said that the rifle, now called SA80-A2, had jammed on numerous occasions.

An army captain who asked not to be identified said that live firing exercises had been carried out on board ships taking them to the Gulf. “In the past, dust and sand have been blamed for jamming, but on ship the conditions were sterile,” he said. “Yet, out of a batch of 24 rifles, nine of them jammed at some point.”

Another soldier from the group said that his rifle had jammed with every fifth round that he fired during live firing in the Kuwaiti desert. Several of the soldiers stripped down their weapons to demonstrate how a thin black metal strip that is meant to release another round into the chamber frequently sticks.

They said that another mechanism, which was supposed to show when the chamber was empty, also jammed, leaving troops unsure whether they still had live ammunition in the magazine. The captain said: “I know we are supposed to count every round we fire, but that is not always possible in the heat of battle.”

The SA80 has been dogged by controversy since it first came into service in 1992, but its failings were supposed to have been rectified by a £58 million modification by the arms manufacturer Heckler & Koch, owned by BAE systems. All 300,000 rifles have been or are being upgraded.

The modifications included a new breech block, breech bolt, cartridge extractor and ejector, firing pin, and cocking handle. The whole magazine was also replaced.

A British army spokesman insisted last night: “The problems experienced by these troops have not been reflected in the extensive trials of the weapons both on land and at sea. The SA80-A2 has so far proved to be a much more reliable weapon than its predecessor. We have also instituted a rigorous new cleaning regime for the modified weapon.”

In Kuwait a senior British officer acknowledged that there had been some problems — but “nothing massive” — with the rifle. Any complaints were being investigated. He insisted that it was wrong to make a judgment about the rifle based on a few random remarks from a soldier.

The claims about the new version of the SA80 rifle were also greeted with surprise by senior army officers at the Ministry of Defence.

They said that 7th Armoured Brigade, the Desert Rats, which has been training with the SA80-A2 for months, before leaving for Kuwait, had praised the rifle. “None of the soldiers complained about jamming, and we feel confident that the SA80-A2 is an excellent weapon, as good as any in the world,” one officer said.

An MoD official said that sometimes soldiers treated the magazines of their rifles in a rough way and they could get damaged. “All they have to do is go to the quartermaster and get another magazine, it’s nothing to do with the rifle as such,” the official said.

The first time that the SA80-A2 was used in combat was by the Royal Marines in Afghanistan. The MoD said that there had been eight reports of weapon failure.

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