As the UK Government denies being told of the dangers of depleted uranium (DU) on its troops in 1997, it has become clear that it was first warned at least a decade ago.

We warned UK troops in the Gulf in 1991

Ministry of Defence And an even earlier warning was issued in the US, a close Nato ally, in 1990.

A BBC radio investigation into DU, Costing the Earth, broadcast 18 months ago, gave details of these and other warnings.

Yet the UK armed forces minister, John Spellar, told Parliament this week that the conclusion of many years' research was that "there is no evidence linking DU to cancers or to the more general ill-health being experienced by some Gulf veterans".

The UK Government has come under increasing pressure to reveal what it knows about the risks of DU, amid reports that it was told of the risks to health several years ago.

It has announced a voluntary screening programme, in line with other European countries.

The 1991 warning came from an official at AEA Technology, the trading name of the UK Atomic Energy Authority.

He sent a document to the Royal Ordnance in London, the company that makes DU ammunition for the Ministry of Defence.

Half a million dead

The document looked at what might happen if all the DU fired in the Gulf War by tanks - about 8% of the total DU used there - were inhaled.

If that happened, it said, the latest International Commission on Radiological Protection risk factor calculated that there could be half a million deaths as a result by 2000.

The Royal Ordnance and the MoD work closely together. An MoD spokeswoman told BBC News Online: "I think it's fair to say we are in day-to-day contact."

The MoD in fact knew that there were some risks associated with DU as long ago as 1979.

Three hundred tonnes of DU were fired in the Gulf War

A spokesman told BBC News Online: "An MoD memo then was clear about both the toxic and the radioactive risks.

"We warned UK troops in the Gulf in 1991 about them, and since 1993 we have publicised our understanding of the risks.

"But this does not change by one iota our stance, or the statement by Mr Spellar two days ago.

"We've known for over 20 years that there are risks. But we don't think those risks are significant."

The 1990 warning came from the US-based Science Applications International Corporation.

It said the short-term effects of high doses of DU could end in death, and the long-term effects of low doses had been implicated in cancer.

There have been other warnings. A 1995 report from the US Army Environmental Policy Institute said: "If DU enters the body, it has the potential to generate significant medical consequences."

DU has been blamed for a number of leukaemia cases among former peacekeepers who served in the Balkans. Veterans also say it contributed to health problems suffered after the Gulf War.

And there is concern for civilians, especially in Iraq, where a huge increase in some forms of cancer and birth defects has been reported since the war ended in 1991.

'Little risk'

DU is a heavy metal, 1.7 times as dense as lead. This makes it a potent weapon for punching through armour, and it is used mainly for attacking tanks and other armoured targets.

The MoD, the Pentagon and Nato maintain that it poses little risk on the battlefield or subsequently, though they do say that troops entering vehicles struck by DU munitions should wear protective clothing.

They argue that the main danger from DU comes from its chemical composition, not from its radioactivity.

Peacekeeping forces are concerned

But it is hard to see how any of them could claim not to have known of the wider risks before the start of the Gulf War.

A memorandum dated 1 March 1991, as the war ended, may be instructive.

Written by a Lt-Col M V Ziehman of Los Alamos National Laboratory in New Mexico, it is headed: "The effectiveness of depleted uranium penetrators."

Defending DU

It reads: "There has been, and continues to be, a concern regarding the impact of DU on the environment.

"Therefore, if no-one makes a case for the effectiveness of DU on the battlefield, DU rounds may become politically unacceptable and thus be deleted from the arsenal.

"If DU penetrators proved their worth during our recent combat activities, then we should assure their future existence (until something better is developed) through Service/Department of Defense proponency.

"If proponency is not garnered, it is possible that we stand to lose a valuable combat capability."