The CAJ's Paul Mageean: Assurances are needed

Mr Stevens is currently heading the investigation into allegations of security force collusion in the loyalist murder of the Belfast solicitor Pat Finucane in 1989.

The Committee on the Administration of Justice said assurances need to be given that Mr Stevens' new job will not distract him from the Finucane inquiry.

Paul McGeean from the CAJ said: ''I think the primary thing that Mr Steven should be do now is to reassure the public and the Finucane family that the appointment to the chief commissioner of the Met will not prejudice the investigation into the Finucane murder.''

However Chris Ryder, a former member of the Northern Ireland Police Authority and author on the Royal Ulster Constabulary said he believes Mr Stevens will complete the Finucane investigation.

Mr Ryder said: ''Mr Stevens is directing and controlling the Finucane murder investigation and as such he has an another six months before he becomes the Metropolitan Police Commissioner.

RUC expert Chris Ryder: Stevens will finish Finucane inquiry

''I think he will continue to direct and control it even if it is not completed by the early part of the year when he assumes his new command.''

John Stevens will replace the current head of Scotland Yard, Paul Condon.

Mr Condon agreed to stand down at the end of his term in post following bad publicity over the botched investigation of the racist murder of a black teenager, Stephen Lawrence.

Mr Stevens first came to Northern Ireland to investigate allegations about collusion between the security forces and loyalist paramilitaries in 1989 in the aftermath of the Finucane murder.

A high profile solicitor, Pat Finucane was shot dead in front of his family at his home in north Belfast.

Collusion charges

As a result of Stevens' inquiries into collusion several members of the security forces were convicted of revealing information on republicans to loyalists, but no-one was charged with the Finucane murder.

Mr Stevens was involved in a second investigation in April 1993 as the allegations continued.

The family of Pat Finucane suspect security force collusion in his murder

Launching the third inquiry into collusion allegations on 29 April this year Stevens made the surprise announcement that he had never investigated the circumstances of the murder of Pat Finucane during his previous inquiries.

Mr Stevens is heading the third inquiry independently of the Royal Ulster Constabulary after he was given responsibility for the investigation by RUC Chief Constable Sir Ronnie Flanagan.

The Stevens inquiry team is currently locked in a court battle with a Northern Ireland journalist.

He is refusing to hand over his notes of interviews with a self confessed loyalist informer who said he gave the RUC special branch information which could have prevented Pat Finucane's murder.

The Sunday Tribune's northern editor, Ed Moloney, published an article detailing his interview with loyalist William Stobie, on 27 June, but has said he will face jail rather than pass on the notes.

Mr Stobie has been charged with the Finucane murder.