FILE PHOTO: Sinn Fein President Gerry Adams delivers a speech at his party's annual conference in Dublin, Ireland November 18, 2017. Picture taken November 18, 2017. REUTERS/Clodagh Kilcoyne/File Photo

BELFAST (Reuters) - Former Sinn Fein leader Gerry Adams lost an appeal on Wednesday to overturn two 1975 convictions for trying to escape from a prison in Northern Ireland after a court dismissed his argument that his initial detention was illegal.

Adams, who stood down as president of the Irish nationalist party on Saturday, was among hundreds of people interned without trial in British-ruled Northern Ireland in the early 1970s under a policy meant to break the guerrilla Irish Republican Army (IRA).

While Adams did not dispute the escape attempts, his lawyers told Belfast’s Royal Courts of Justice last month that he had not been lawfully detained in the first place and so could not be convicted of escaping from legal custody.

They argued that the internment order had not been considered by a British Secretary of State, as it should have been, but by a junior minister. That was dismissed by the three-judge panel on Wednesday.

“This court has been satisfied as to the validity of the ICO (Interim Custody Order) made by the Minister on behalf of the Secretary of State. Accordingly the court is satisfied that the convictions are safe. The appeal is dismissed,” Justice Ronald Weatherup told the court.

Adams, who has always denied membership of the IRA, was detained in Belfast’s Maze prison in 1973. On one of his attempts to flee, he switched places with a visitor at the prison who had been abducted while waiting at a bus stop.

The court heard that a man who bore a resemblance to Adams had been taken against his will to a house where his hair was dyed and he was given a false beard. The substitution was spotted by prison staff.

Adams, who took over as leader of Sinn Fein in 1983 when it was at the time the IRA’s political wing, was sentenced to 18 months in jail for attempting to escape.