The King must personally deliver the new medal to nuclear veterans - along with a promise of compensation, the government has been told.
Veterans Minister Johnny Mercer has been urged to ensure that King Charles presides at a ceremony honouring the Cold War heroes before Remembrance Sunday.
"The newly-minted nuclear test medal is very fine, and we commend the government for finally agreeing to issue it," campaigning Manchester councillor Tommy Judge told him in a letter. "But frankly it is not enough."
He said the veterans' "invaluable contribution has often come at a terrible price", with veterans proven to have higher rates of death and cancer, miscarriages in their wives, and infant mortality and birth defects in their children.
Cllr Judge said compensation was "long overdue" and in the US, Joe Biden recently extended a $75,000-a-head scheme. "Nuclear test veterans are getting old. They cannot wait any longer for recompense - the time to do this is now," said Cllr Judge, who is a representative of the Nuclear-Free Local Authorities.
He added: "The test veteran community, and the charities that fight for them, have for many years reported instances of cancer, often repeated, and premature death amongst veterans and many profound disabilities amongst their offspring. Many people believe that this was the result of exposure to radiation in these tests.
“The Secretary of State has yet to make any promise of compensation for the suffering and chronic ill-health caused to veterans or their children, nor recompense for the wives and families whose husbands and fathers died too young. We believe that the time to do so is long overdue and that it is now”.
Government officials are believed to be in discussions with Buckingham Palace about arranging a ceremony. An event was requested last November on the day the medal was announced, but despite the fact that the king's diary is decided months in advance, it is thought a formal request has been made only recently.
Campaigners fear the official request may have come too late to fit in His Majesty's schedule, although courtiers have previously said he was keen to oversee any ceremony.
Cllr Judge said: "Ironically, British service personnel who participated in joint tests with US forces and who meet the eligibility criteria can automatically access this the payment from the Government of the United States, but from the UK Government they automatically receive nothing. Instead, they must go through a long- and uncertain process, and many hoops, to seek a service pension. The disparity in treatment seems manifestly unfair."
Labour and the Tories have been asked to authorise automatic war pensions and a compensation scheme. The government has refused to consider it and Labour has yet to decide its next manifesto.
Cllr Judge said: "Nuclear test veterans are getting old. They cannot wait any longer for recompense – the time to do this is now alongside the award of a service medal. They need to pay up."