The Irish nationalist party, Sinn Fein expelled a senior member yesterday after he admitted he had been spying for Britain for two decades.

Denis Donaldson was cleared last week of spying for Sinn Fein which seeks to end British rule in Northern Ireland. In fact, he said, he had been a British agent for 20 years.

Irish Prime Minister Bertie Ahern called it a "bizarre twist".

"I was a British agent at the time. I was recruited in the 1980s after compromising myself during a vulnerable time in my life," Mr Donaldson, formerly Sinn Fein's head of administration at the mothballed Stormont Assembly in British-ruled Northern Ireland, told Irish state broadcaster RTE.

Since that time, Mr Donaldson said, he had worked for British intelligence and Northern Irish police.

"Over that period, I was paid money," he said. Mr Donaldson said he deeply regretted his activities and apologised to his family and the Republican movement.

Sinn Fein President Gerry Adams told reporters at a news conference in Dublin that Mr Donaldson had approached the party after police informed him his cover was about to be blown and his life was in danger.

The British government declined to comment on the revelations.