The Garda Siochana Om­budsman Commission (GSOC) is to give the go-ahead for a major inquiry into allegations of an improper relationship between a convicted drug dealer and senior gardaí.

The Sunday Tribune has learned that in recent days the ombudsman has begun investigations with a view to establishing a public interest inquiry into the circumstances surrounding the dropping of drug trafficking charges against Kieran Boylan from Ardee in Co Louth.

It is understood that the investigation will run parallel to a garda probe which is currently taking place in Store Street garda station led by assistant commissioner Michael McCarthy. It is expected to be announced within the next 10 days.

Last July, on the day that the courts recessed for summer break, it was announced that the case against 37-year-old Boylan for possession of €1.7 million worth of heroin and cocaine in October 2005, was being struck out.

A barrister for the DPP said the decision had been taking at the highest level but offered no other information.

There have been allegations that the top tier of garda management was responsible after Boylan threatened to reveal his relations with senior members of the force if he was prosecuted.

Boylan has alleged that he was a garda informant and had participated in entrapment operations where gardaí delivered drugs he supplied to petty criminals who were later arrested.

He has previously bragged that he was a garda agent who was untouchable by the law.

There has been considerable political pressure on the Ombudsman to investigate the relationship for several months. A spokesman would not confirm that the probe has been given the go ahead but said it is still under consideration.

Boylan has named members of the gardaí that he was allegedly working in tandem with and if it is found that the officers acted improperly they could face dismissal.

There are also fears that such a wide-sweeping investigation could open a Pandoras box about the way certain garda investigations are handled in the wider public interest.

There have been long held suspicions that certain drug dealers are allowed to operate in return for offering other dealers up for prosecution.

Garda sources say that the Boylan inquiry has the potential to be more damaging than the garda corruption in Donegal.

The garda ombudsman's first public interest inquiry was launched into the circumstances of the death Terence Wheelock, who was found hanging in a garda cell in 2005.

It is expected to be completed in the coming months. It's second public interest investigation, which has yet to be formally announced but is under way, is probing the 2005 death of pensioner Mary Seavers killed by an out-of-control garda car in Dublin.