Former serviceman Geoffrey Thorne today called a High Court settlement over the death of a comrade killed in nerve gas experiments "another cover-up".

Mr Thorne, now 75, was a 23-year-old RAF engineer when he volunteered to take part in top secret Ministry of Defence trials at Porton Down in Wiltshire.

The Birstall man believed he was helping to find a cure for the common cold. It was not until two years ago, at a second inquest into the death of a young airman, that he discovered he and hundreds of others had been exposed to deadly nerve gas Sarin.

That inquest ruled 20-year-old Leading Aircraftsman Ronald Maddison had been unlawfully killed.

An original inquest in 1953 had reached a misadventure verdict but, in 2002, the High Court quashed that and ordered the new inquest, which took place in 2004.

Dissatisfied with the new "unlawful killing" verdict, the MoD had been due to seek a judicial review this week but withdrew its application when a settlement was reached.

It agreed to accept the 2004 verdict - but only on the basis that Mr Maddison had died as a result of "gross negligence" in respect of the "conduct and planning" of the experiment.

MoD lawyers successfully argued that the new verdict could not imply Mr Maddison did not consent to the experiment or there had been a failure to obtain his consent.

But Mr Thorne, of Lea View, a grandfather of eight who is a member of the Porton Down Veterans Support Group which campaigns for compensation, says that the settlement is a cover-up.

He says it hides the argument that Mr Maddison, and the rest had not given informed consent to being exposed to the deadly nerve agent.

"What the MoD did to us was a national disgrace," he said. "They used servicemen as human guinea pigs and covered it up for more than 50 years. This was another cover-up.

"We were willing to die for our country but not in that way. None of us expected to be exposed to lethal nerve agents by our own side. We would not have volunteered if we had known what we know now."

And he added: "A lot of the facts only came out at the inquest two years ago. It turned out the week before I went to Porton Down two men who had had the same trials as me had to be revived after their hearts stopped beating.

"If I had known that then, I would have packed my bags and gone straight home.

"The truth is we were duped. Those tests should never have been carried out without any of us giving our fully informed consent."

In return for taking part Mr Thorne was given 15 shillings and a week's leave.

He said there were daily tests by scientists at Porton Down, including being photographed naked, but the most memorable was when the group was given gas masks and led into a sealed chamber where scientists dropped liquid onto a piece of material strapped to their arms.

"It turned out that was the Sarin," he said. "I had 20 drops; they wanted to see if it soaked through the uniform material and then the next day we had to go back and they scraped bits off our skin."

Now Mr Thorne fears his failing health, which began to deteriorate when he was 40, could be the long-term result .

"I've no proof but it's a fear that niggles away at the back of my head," he said. "They know the short-term effect of Sarin is that it can kill but no one knows what the long-term effects could be."

Eric Gow, chairman of the Porton Down Veterans Group, has objected to the compromise and has vowed to fight on.