Labour leader Eamon Gilmore said it was "unbelievable" that Ms Harney did not know the scale of the Tallaght Hospital X-ray controversy until this week, given that it first came to light early last year.

Mr Gilmore said it was the latest in a long list of blunders in the healthcare system where nothing was done about them about until they were publicly-exposed.

"The country has had enough of the mismanagement of the health service, this sequence of things going wrong in the health service and nothing being done about it until it becomes public," he said. "It is the same pattern all of the time."

Mr Gilmore said it was time for Ms Harney - who is in New Zealand for St Patrick's Day celebrations - to be removed from the health ministry.

"I have a lot of time for her, she has been a very competent minister in other areas, but she has been a hopeless minister for health, and I think it is time she was moved."

Fine Gael's health spokesman Dr James Reilly demanded Ms Harney return to Ireland and resign.

The Taoiseach refused to be drawn on his plans for a reshuffle but defended Ms Harney as a proactive and reforming health minister who had done more than any of her predecessors to overhaul the health service.

Fine Gael leader Enda Kenny said it was "unconscionable" that a number of people more than twice the population of Co Leitrim should not have their x-rays read over a four year period. "It smacks of a gigantic cover up that only those who had problems would be informed," he said. "There is the possibility of sizeable numbers walking around with tumours undetected or other problems because X-rays have not been read by radiologists."

Accusing Ms Harney of washing her hands of the scandal, Mr Kenny said she would not be removed from the Cabinet because Fianna Fail could not then rely on her vote to prop up the Government.