Nearly 1,000 former servicemen who suffered as a result of British nuclear tests in the South Pacific more than 50 years ago yesterday took their fight for compensation to the High Court.

The 970 British, New Zealand and Fijian claimants say they have suffered illnesses such as cancers, skin defects and fertility problems as a result of fallout from atomic bomb tests.

At the start of a three-week hearing the veterans' counsel said new scientific evidence had linked ill-health with those who participated or were present.

Benjamin Browne QC said the Government had accepted the validity of a study of New Zealand test veterans which proved that most if not all had suffered genetic effects due to radiation exposure.

And a leading American expert said studies of Japanese atomic bomb survivors showed that exposure to radiation at the levels of the British tests substantially increased cancer risk.

Former members of all three Armed Services, including a number of veterans from the West region, are seeking justice after saying they were exposed to harmful radiation without protection.

Claims running into many millions of pounds relate to bomb testing in mainland Australia and the Pacific by the Ministry of Defence at the height of the Cold War in the 1950s.

The claimants include British Nuclear Test Veterans' Association (BNTVA) member Jeff Liddiatt, 68, of Portishead, who believes his degenerating spinal condition was a direct result of the tests.

Mr Liddiatt was a leading aircraftsman stationed at Maralinga in Australia in the early 1950s when he was exposed without protection to "nuclear debris everywhere" at detonation sites.

Outside London's High Court yesterday, he told the Western Daily Press: "It's got nothing to do with anger, we just want honesty and justice."

Mr Liddiatt, who has undergone several major operations for his condition, was among 150 veterans who packed the courtroom and is one of 10 due to give evidence.

For the BNTVA, Mr Browne told Mr Justice Foskett that about 25,000 members of the UK, Australian and New Zealand Armed Forces took part in the tests – some an active part but very many as bystanders.

He said: "The government had not only the awful lessons of Hiroshima and Nagasaki, but also scientific evidence as to the costs and risks of radiation.

"The Medical Research Council had advised that 'even the smallest dose of radiation produces a genetic effect'."

Mr Browne said the UK government had throughout maintained that "very few, if any, of the participants were exposed to thermonuclear fallout".

He went on: "We say that we will be able to demonstrate the government's case is wrong."

He said it was now apparent that those responsible for the tests did not really understand what risks were entailed.

Giving examples, he said that in one explosion the yield of the bomb was probably 70 times higher than anticipated.

In another, the scientists responsible were said to be "nonplussed with the amount of radioactivity registered" and were "most apologetic".

An MoD spokesman said it was unable to comment as the case was ongoing.