Hundreds of ex-servicemen who say they were made ill as a result of being exposed to radiation during British nuclear weapons tests in the 1950s have lost their Supreme Court bid to be able to launch damages claims against the Ministry of Defence.
More than 1,000 veterans want compensation and have been battling for permission to launch damages claims for some two years.
Although today's judgment blocks most claims, a certain number can still proceed because of an earlier legal ruling.
The veterans took their fight to the Supreme Court - the highest court in the UK - in November after battles in the High Court and the Court of Appeal.
In 2009, 10 "lead" claimants won the first round of the veterans' battle when a High Court judge said claims could go ahead.
But the MoD appealed and, in 2010, a Court of Appeal ruling blocked nine of the 10 lead claims when judges said they were "statute-barred" because they had been made too late.
A challenge by the veterans against that Court of Appeal decision was rejected today by Supreme Court justices by a four-to-three majority.
Veterans blame ill-health - including cancer, skin defects and fertility problems - on their involvement in British nuclear tests in Australia, on Christmas Island and in the Pacific Ocean between 1952 and 1958.
The MoD acknowledges a "debt of gratitude" but denies negligence.
Lord Wilson, one of the judges who rejected the appeal, ruled that the actions had "no real prospect of success".
Lord Wilson said, after reading out a summary of the court's decision: "Putting aside the law for one moment, all seven members of the court would wish to record their personal sympathy for the veterans."
He said: "It must be bad enough for the nine veterans, and the other claimants, to learn that they have lost this final round, but to learn that they have lost by the narrowest possible margin must make it even worse."
The panel was made up of Supreme Court president Lord Phillips, Lord Walker, Lady Hale, Lord Brown, Lord Mance, Lord Kerr and Lord Wilson.
Lawyers said they were calculating how many veterans, or their families, would still be able to launch damages claims in the High Court and estimated that the number could still be in the hundreds.
They said the fight for "justice" would go on and urged the Government to set up a compensation scheme.
Veterans' families said they were disappointed with the ruling and called on ministers to acknowledge that servicemen had been "put at risk" and should be compensated.