FLASHBACK: The army asked me to make bombs for the IRA, told me I had the Prime Minister's blessing ... then tried to kill me

DUBLIN (Reuters) - Northern Ireland's unionist politicians have demanded a public inquiry into revelations that a senior member of Sinn Fein was a British spy for more than 20 years.

Sinn Fein, political ally of the IRA, expelled party veteran Denis Donaldson, 55, on Friday after he admitted being a paid agent for British intelligence and the province's police Special Branch since the 1980s.

The admission, described as a "bizarre twist" by Prime Minister Bertie Ahern, came just a week after Donaldson was cleared of spying for Sinn Fein.

"A full public inquiry is the only way we can really get to the bottom of this -- there's just too many unanswered questions," a spokesman for the Ulster Unionist Party said on Saturday.

The Democratic Unionist Party called on the British government to make a statement.

The arrest of Donaldson and two others accused of being part of a Sinn Fein spy ring in 2002 led to the collapse of the province's Protestant-Catholic power-sharing assembly at Stormont in Belfast, an affair that came to be known locally as "Stormontgate".

Last week the Director of Public Prosecutions decided it was "no longer in the public interest" to pursue the case.

In his statement on Friday -- made, he said, after police warned him his cover was about to be blown -- Donaldson said there had been no spy ring at Stormont and that Stormontgate was "a scam and a fiction created by Special Branch".

The Northern Ireland Office has denied the Stormont raid was politically motivated, saying it had been purely to prevent paramilitary intelligence gathering.

Donaldson, formerly Sinn Fein's head of administration at Stormont, said he deeply regretted his activities and apologised to his family and the Republican movement.

Sinn Fein leader Gerry Adams accused elements within the British intelligence services of trying to undermine 1998's Good Friday peace accord as they were unhappy at changes that have largely ended 30 years of violence between Irish republican and pro-British paramilitaries.

"Those who ran those agencies ... they hate republicans with a passion. For them the war isn't over, for them Good Friday (Agreement) was a huge mistake," Adams told a news conference in Dublin on Friday.

He said it was too soon to say what the consequences would be in terms of kick-starting stalled talks on restoring the Belfast assembly.