Alleged IRA bomber John Downey has been arrested in Co Donegal on suspicion of murdering two Ulster Defence Regiment (UDR) soldiers in Enniskillen in 1972.

The 66-year-old is also being held on suspicion of aiding and abetting an explosion. He is expected to appear at the High Court in Dublin on Tuesday.

Lance Corporal Alfred Johnston - a father of four - and Private James Eames - who had three children - died when a device exploded in a car they were checking on the Irvinestown Road, Cherrymount, Enniskillen in 1972.

Detective Chief Inspector John Caldwell said “the PSNI investigation into these murders remains active”.

The arrest was made under a European Arrest Warrant as part of a joint operation with the PSNI.

Mr Downey’s trial on charges linked to the 1982 London Hyde Park bombing which killed four soldiers and seven horses collapsed in February 2014.

He had been mistakenly sent a government letter saying he was not wanted for questioning by police when in fact there was an outstanding warrant against him. The full scale of the scheme involving other republican paramilitary On The Run suspects then emerged.

The court’s ruling sparked a political crisis at Stormont with the then first minister Peter Robinson threatening to resign unless the British government held an inquiry into the provision of letters of comfort to republicans who are on-the-run.

A judge-led review was promised by then prime minister David Cameron.

A spokesman for the Public Prosecution Service for Northern Ireland said: “Following careful consideration of all available evidence, a decision has been taken to prosecute one person for the offence of murder and for aiding and abetting the causing of an explosion.

“Extradition proceedings were initiated in the High Court in Dublin on Monday November 5, to seek the extradition of one man from the Republic of Ireland for trial in Northern Ireland.

“One man was subsequently arrested in County Donegal this evening and is due to appear in court in Dublin tomorrow.”

On July 20th, 1982, a car bomb left in South Carriage Drive killed four British soldiers as they rode through Hyde Park in central London to the changing of the guard.

Seven horses were also killed as the soldiers travelled from their barracks to Buckingham Palace. Another horse survived terrible injuries .

The investigation into the bombing led police to Mr Downey, through fingerprints on parking tickets and a description given by witnesses of two men carrying out reconnaissance in the area before the attack.

An arrest warrant was issued, but it was decided not to seek Mr Downey’s extradition from the Republic in 1989, in part due to the lack of strong evidence against him, the court was told.

Then in 2007, Mr Downey received assurance he was not at risk of prosecution as part of a scheme run by the PSNI. He was one of 187 On the Runs (OTRs) to seek clarification from the authorities in the wake of the Belfast Agreement.

The court was told by Mr Downey’s legal team that there were other factors, aside from the clerical error, that meant he should not face trial.

These included the length of time — more than 30 years — since the offence, as well as the commitment in 2001 not to pursue those who might benefit from early release schemes.

Mr Downey has always denied any involvement in the Hyde Park attack.