WHEN the Government announced it was opening a telephone inquiry line for the 20,000 servicemen who acted as ill-informed guinea pigs at Porton Down Chemical and Biological Defence Establishment in the Fifties, I decided to call. It was my chance to discover what I was exposed to as an 18-year-old national serviceman.

It was in 1952 at an RAF base just outside York that I read that an extra week's pay would be given to volunteers willing to go for a week to an establishment on Salisbury Plain. And to get there meant travelling first to London, my home town, providing me with the opportunity of two consecutive weekend leaves. It was in that casual manner that thousands of young men endangered their well-being. Some have maintained that subsequent illnesses have been linked to their experience.

There was no verbal mention of nasty things like nerve or any other toxic gas, chemical or biological warfare, but together with the 20 or so other fresh-faced youths I joined that Sunday in deepest Wiltshire I was asked to sign a piece of paper stating that I was offering my services willingly.

That first evening we attended the Naafi and spent some of our extra week's pay on a concoction called black velvet. There was scant discussion of why we were there.

On the first occasion I was called into the laboratories I was asked to sit outside a chamber the size of a small room and breathe some through a mouthpiece which protruded from its glass wall. On the second occasion, two or three days later, I went for a blood test. I felt nothing except the prick of a needle.

The guinea pigs have now been told they will be sent a summary of their records, providing it is considered that doing so will not breach security. I feel fine, even nearly 50 years later, and I am merely curious about my own particular inhalation, but the helpline operator said she is doubtful whether they would tell me what it was.

I suppose, speaking personally, if you've waited all those years to know, another year or two won't matter. But for others among the 20,000 it might well be a matter of life or death, or at least a more comfortable last few years.

The hotline is 0845 6039140.