In the world's worst civil nuclear disaster, Chernobyl exploded on April 26, 1986, and its radioactive contamination was blamed for thousands of deaths in Ukraine, Belarus and Russia, and for a huge increase in thyroid cancer.

The Sellafield reprocessing plant, on England's northwest coast across the Irish Sea, has long caused friction between the two governments due to Irish fears of accidents or pollution.

"Tony, Look me in the eye and tell me I'm safe," said Hewson's postcard to Blair under a picture of a staring green eye. It was one of more than 1.2 million such postcards sent by Irish households for delivery to Britain last week.

Long a focus of protests for environmentalists in Britain and Ireland, the anti-Sellafield lobby say the issue has taken on new urgency since the Sept. 11 attacks on the United States.

"That's the reason that people are re-thinking exactly the problems of Sellafield," said Hewson, whose husband Bono, of the U2 band, is a leading campaigner against Third World debt.

"It has 75 tonnes of plutonium sitting on its site. It can't but be at the top of any terrorist's list," she added.

Britain, which also faces pressure over Sellafield from other European nations, said it recognized the sincerity of Irish concerns but insisted the risks were minimal

Energy Minister Brian Wilson issued a statement decrying the "emotive and misleading arguments" of anti-Sellafield campaigners and citing "facts and evidence produced from reputable scientific sources about the negligible impacts of activities at Sellafield."

"The U.K. government would not pursue any course of action which is damaging either to our own people or to our neighbours in Ireland," he said.

As well as Hewson, a string of other well-known figures including pop group The Corrs, singers Ronan Keating and Samantha Mumba and Manchester United soccer captain Roy Keane, have backed the Sellafield postcard protest.

Like Blair, Prince Charles' office was also receiving last week sacks full of the mass-produced postcards, his showing a pink-tinged holocaust landscape with the words "Greetings from Ireland ... wish you were here?"

Norman Askew, chairman of Sellafield's owner British Nuclear Fuels, is also being targeted by the campaign, which is backed by the Irish government.

"Tell us the truth," the postcard aimed at him said over a pair of lips. "You know that radiation released into the atmosphere has no borders ... No country, no government and no company can afford this risk for profit."