Relatives of murdered British agent Denis Donaldson are to take legal action against the Irish state.

An inquest into the Belfast man’s killing in April 2006 was adjourned for a ninth time in Letterkenny yesterday.

A former senior member of Sinn Féin, Mr Donaldson (56) was shot dead at a family holiday home near Glenties in Co Donegal months after it emerged that he had acted as a British agent for the previous 20 years.

At a reconvened inquest into his death yesterday, investigating gardai requested a further adjournment to allow a file to be completed for the Republic’s Director of Public Prosecutions.

Garda Superintendent Michael Finnan told coroner Denis McCauley the file would be ready within weeks.

But the Donaldsons’ family solicitor, Ciaran Shields of Madden and Finucane, said the delay in conducting the inquest was unacceptable.

He said the family now intended taking action against the state under Article 2 of the European Convention on Human Rights which protects the right to life.

The development came after Mr Donaldson’s daughter Jane called for evidence held by all state agencies north and south of the border to be disclosed.

In a letter to The Irish Times on Monday, Ms Donaldson said the true story of her father’s death was still being written and the role of senior police officers was central to any investigation.

“In particular, attention has been drawn to the activities of a person known as ‘Lenny’, the Special Branch handler who maintained communication with Denis until his murder,” she said.

The Belfast woman claimed ‘Lenny’ knew where her father was living in Co Donegal and had vital evidence about his murder.

“The Garda Siochana has vigorously opposed the commencement of inquest proceedings into Denis’s murder on grounds that it has a live investigation under way,” Ms Donaldson wrote.

“Such claims stretch credulity amidst many unanswered questions about the independence and effectiveness of this Garda investigation.”

Mr McCauley adjourned the inquest until November 8.