The family of a young RAF mechanic who died after taking part in a secret nerve gas test will seek compensation following a ruling that he was unlawfully killed.

The verdict into the death of Ronald Maddison, from Consett, County Durham, returned by an inquest jury yesterday, paves the way for a series of legal claims against the Ministry of Defence and a compensation claim by his family.

Mr Maddison died aged 20 after having drops of sarin dabbed on his arm at Porton Down chemical warfare testing facility, in Wiltshire, in 1953.

Winston Churchill's government ordered the initial inquest, which reached a verdict of misadventure, to be held in secret.

But after years of campaigning, an inquiry was launched by Wiltshire Police in 1999. In 2002, Lord Chief Justice Woolf granted permission for a second inquest, which began in May this year.

Alan Care, lawyer for the Maddison family, said the verdict brought to an end a 50-year call for an explanation about why the airman died.

Mr Care said: "The family now seek compensation which, as the Treasury solicitor had indicated in 1953, should be paid to the family."

Lillias Craik, Mr Maddison's sister, said her father could not tell her what he learned about her brother's death when he attended the first inquest because he was sworn to secrecy.

She said: "I asked him what had happened. All he said was, 'If I tell you what I know, I could go to jail, because I have signed the Official Secrets Act'."

Mrs Craik said the truth was difficult to accept, but she was pleased it was out.

"I feel so angry. It is hard to direct it at anyone because they all did it: the scientists, the MoD, all of them. It's wrong, it's wrong.

"We are a civilised bloody country, for God's sake."

A spokesman for the MoD said: "The Ministry of Defence notes the jury's findings and will now take some time to reflect on these.

"We will be seeking legal advice on whether we wish to consider a judicial review."

Veteran Terry Alderson, 74, from Danby, near Whitby, North Yorkshire, said he was delighted with the decision and was now calling for a public inquiry and a full apology from the Government.

Ian Foulkes, 40, from Chippenham, Wiltshire, was tested with sarin as recently as 1983.

He said after the hearing: "I think now there will be claims for compensation from the other veterans because their health has been affected."