Scientists are poised to start the first independent investigation into the effects of chemical warfare tests on 23,000 human "guinea pigs".

The Ministry of Defence's top secret Porton Down research centre has asked the Medical Research Council to help assess the impact of its experiments. Thousands of servicemen and women who volunteered for research into the common cold claim they were tricked into taking agents including nerve gas and LSD.

Many who suffered after tests made between 1940 and 1989 at the Wiltshire centre are threatening to sue the MoD.

They were offered medical assessments by the MoD last year but have held out for an independent inquiry.

A Porton Down spokesperson said there had been concerns about the long-term problems and the MRC had been asked to help with an independent assessment of records. The move has been welcomed by campaigners, including Labour MP Tam Dalyell, who said volunteers had a right to know what had happened to them.

Wiltshire Police are pursuing a corporate manslaughter investigation into Porton Down sparked by a Sunderland man. Gordon Bell began his campaign after looking into the death of Consett airman Ronald Maddison, who died, aged 20, during a nerve agent testing session in 1953.

Mr Bell believes his own chronic skin complaint stems from his days at the centre. Mr Maddison died when 200mg of a nerve gas was dripped on to uniform material taped to his arm during experiments. Ex-military personnel are also battling for a change in the law to allow them to claim compensation after the Government lifted the MoD's legal immunity.

Other victims include wheelchair-bound Alan Walton, 66, of Cramlington, who developed multiple sclerosis two years after he left the RAF in 1958.

Mr Walton has told The Journal how he was given mustard gas at Porton Down.

"When I came out, I thought I was dying, I had watering eyes which I sometimes still get. And I get out of breath at times," he said. "I began to suffer bouts of severe depression ... I've contacted Porton Down for my records recently but they said they can't find them.

"You would at least think the Government would do routine checks on your health after they had put you in the gas chamber, but they haven't even done that."

Sunderland University chemist Prof Malcolm Hooper has accused the MoD of covering up the effects of atomic and chemical tests on Porton Down and Gulf War soldiers.

   The US has same sort of experiments on indigenous persons in Panama and elsewhere to deal with.