A former RAF navigator has claimed the size of a nuclear bomb detonated during tests in the 1950s could have been three times bigger than the Government officially stated, in evidence which could that prove crucial for more than 1,000 service veterans suing the Ministry of Defence (MoD) for upwards of £100m.
Flight Lieutenant Joseph Pasquini, who served in the RAF's 76 Squadron, took measurements during the UK's biggest nuclear test blast at Christmas Island in the Pacific on 28 April, 1958 – known as Grapple Y.
Mr Pasquini, who was recording measurements in a Canberra bomber 46,000 ft above the blast, claims he was told the size of the bomb was "in the 10 megaton range", more than three times bigger than the 3.2 megatons the MoD has officially stated – and nearly a hundred times bigger than the atomic bomb dropped by the US on Hiroshima in 1945.
Breaking a 50-year silence because of his anger at the way the veterans have been treated, he added that official records showing how much radiation aircrews were exposed to had been altered and film badges, used to measure radiation, were inaccurate.
Solicitors fighting the MoD on behalf of veterans – who claim that during the 1950s and 1960s they were exposed to unsafe levels of radiation in tests in the Pacific and Australia, leading to cancers and other medical problems – said his evidence could be "significant".
Today, after more than two years of legal wrangling, a four-day hearing begins at the Supreme Court in which nine test cases out of a total 1,011 claimants could win the right to sue the MoD.
The MoD's defence, that the claimants could not sue after three years of discovering their injuries (under the terms of the Limitation Act), was upheld by the Appeal Court last year, but in July the Supreme Court allowed the claimants to appeal this decision.
Regardless of the outcome, the separate claims of the remaining 1,002 claimants are due to go through the High Court next year.
Now aged 78 and living in the US, Mr Pasquini, who is not a claimant, said it was "a miracle" he was still alive after battling cancer for 12 years. He said as his plane flew through the hydrogen cloud after the detonation, his job was to gain samples for scientists.
"I was told that the bomb was in the 10-megaton range by people from the Atomic Weapons Results Establishment (AWRE)," he said. "Radioactive rain fell when Grapple Yankee was detonated. I flew through it and my radiation recording instruments immediately lit up like a Christmas tree."
He claimed that the levels of exposure to radiation for aircrew were "massively understated". "Official readings recorded in the AWRE records were far lower than my logs," Mr Pasquini said. "My readings were... recorded and logged at the time and on the day of the detonation. But they are much higher than the official logs. I have those logs and I am happy to go public with them."
He added: "I made several Freedom of Information requests and looked at the readings officially given and they were utterly false. My records for the MoD and AWRE are inaccurate.
"I didn't say anything for 50 years because I was sworn to secrecy by the Official Secrets Act, and not even my wife knew what I knew. But people need to know the truth about what happened."
Mr Pasquini said that film badges given to aircrews to measure radiation were unreliable. "The film badge only recorded two dimensions," he said. "So if you have one pinned to your chest, it would only pick up radiation in front of you and behind you. But it would not record radiation emanating from above, below or from each two sides."
A spokesman for Rosenblatt solicitors, which is representing veterans from the UK, New Zealand and Fiji since taking up the case six years ago, said: "This is potentially very significant information for the progress of the case."
An MoD spokesman said: "We cannot comment on the details of ongoing individual cases but we recognise the invaluable contribution of all Service personnel who took part in the nuclear testing programme. We are grateful to them for the part they played in ensuring UK security."