Sinn Féin deputy leader Mary Lou McDonald has said the makers of a BBC Spotlight programme in which an alleged former British agent claimed Gerry Adams had ordered the killing of an IRA informer should make the identity of their source known to gardaí.

Ms McDonald said claims made by a "self-proclaimed" informant that Sinn Féin leader Mr Adams was involved in the murder of Denis Donaldson were a "ball of smoke".

She said the allegations had taken on the status of verified truth, despite being based on the word of an anonymous source.

Ms McDonald said the journalists involved should make that person known to gardaí investigating Mr Donaldson’s murder.

She said: “I know journalists jealously guard their sources. It is one of the central pillars of the work you do and there is good reason for it.

“But in circumstances like this where there is a live Garda investigation, if people claim that they have information or evidence the most appropriate people to bring that to is An Garda Síochána.”

Mr Donaldson, a former Sinn Féin group administrator at the Stormont Assembly, was shot dead in Co Donegal in April 2006 after he confessed to being a British agent, which directly led to the collapse of Stormont's institutions.

His killing, which was claimed three years later by the splinter Real IRA, has still not resulted in prosecutions. His inquest has been repeatedly postponed on foot of applications by gardaí.

The man, who infiltrated the IRA for over a decade, was interviewed over months by the BBC’s Spotlight programme.

He claims to have worked for the RUC special branch from 1997 – one of up to 1,000 informers of different levels of importance who were allegedly passing on information about the IRA’s activities.

Ms McDonald said the allegations are without foundation and insisted no fair or reasonable person would accept them.

She said Mr Adams often addresses questions about the past with party members.

However she stressed this allegation was unsubstantiated and was based on a hunch.

The Dublin Central TD said: “Given the seriousness of any person’s involvement in the killing of another it seems extraordinary that mainstream media so readily leap on this and so readily take it as read that the allegation has any basis in fact. It does not.

“Gerry has answered questions. If he is asked questions he will answer them. “

Ms McDonald said Mr Donaldson’s family deserve to know what happened to him and encouraged the gardaí to “do their job”.

She added: “The people who carried this out need to be brought to buck.

“That objective is not assisted by launching broadsides against Gerry Adams.”