LONDON, Feb 25 (Reuters) - An Irishman accused of a bombing that killed four soldiers on horseback in London in 1982 walked free on Tuesday after it emerged at his trial that Northern Irish police had given him a false assurance that he would not be prosecuted.
John Downey, 62, from County Donegal in Ireland, was charged with murdering four members of the Royal Household Cavalry who were killed when a car bomb exploded in Hyde Park as they paraded towards Buckingham Palace. He denied the charges.
Another 23 soldiers from the Household Cavalry, the Queen's official bodyguard, which carries out ceremonial duties on state occasions, were wounded by shrapnel.
Later on the same day, July 20, a second bomb exploded under a bandstand in London's Regent's Park during a performance by the Royal Green Jackets military band, killing seven members.
The Irish Republican Army claimed responsibility for the double bombing, one of its most devastating attacks on the British mainland during the IRA's guerrilla campaign to drive British forces out of the province of Northern Ireland.
Downey's defence had maintained that the trial should not go ahead because he had received a letter of assurance from the Northern Ireland Office in 2007 that he was not wanted in London in connection with the bombing.
"There are no warrants in existence, nor are you wanted in Northern Ireland for arrest, questioning or charging by police. The Police Service of Northern Ireland are not aware of any interest in you by any other police force," the letter said.
But that assurance was hollow, defence lawyers said. London police had never lost interest in arresting Downey and last May they detained him at Gatwick Airport en route to Greece.
The presiding judge in the Old Bailey court hearing Downey's case ruled that the false assurance was a "catastrophic failure" that misled the defendant and a trial would be an abuse of executive power.
The families of those killed said the judgment had left them feeling "great sadness and bitter disappointment".
"This news has left us all feeling devastatingly left down, even more so when the monumental blunder behind this judgement lies at the feet of the Police Service of Northern Ireland," they said in a statement carried by the BBC.
The former Chief Constable of Northern Ireland, Hugh Orde, apologised to the families for "erroneous information being sent to Mr Downey by the Northern Ireland Office and thus prejudicing the current indictment".
London's Metropolitan Police said the case remained open and any more information coming to light would be investigated.
A 1998 peace deal largely ended more than three decades of violence in which more than 3,500 people were killed. The IRA later disbanded, but dissident groups continue to carry out sporadic gun and bomb attacks in Northern Ireland. (Reporting by Stephen Addison; Editing by Mark Heinrich)