The trial of a man accused of bombing Hyde Park in London for the IRA has been dropped after the judge was told about a secret deal granting him immunity.

John Downey (62) had been charged with the murders of the four members of the Household Cavalry who died in the attack in 1982.

The case was thrown out last Friday but we can only now report the decision.

In dismissing the case, Mr. Justice Sweeney said it was a rare case which "offends the court's sense of justice and propriety to be asked to try the defendant".

He said even allowing for the feelings of the victims and their families, and the desire to see someone put on trial, there was "greater public interest in holding officials of the state to promises they have made in full understanding of what is involved in the bargain".

The families of the victims say they feel "devastatingly let down".

Northern Ireland Secretary Theresa Villiers says Police in Northern Ireland should reflect on "the serious error" following the collapse.

The relatives of soldiers Roy Bright, Anthony "Denis" Daly, Simon Tipper and Jeffrey Young said they "never ceased in their desire to see that justice be done".

They said that the grieving for the fallen soldiers "never stops", adding "The torment for the families will be ongoing, knowing that John Downey will be returning to his family and life will be normal for him".

Reporter Ian Woods is at the High Court in London.

The Hyde Park attack on July 20th 1982 provided some of the most vivid images of the IRA bombing campaign in mainland Britain.

The Blues and Royals regiment of the Household Cavalry were making their daily procession from their barracks in Kensington, to the Changing of the Guard ceremony at Buckingham Palace.

They were accompanied by two mounted police officers.

Up to 25lbs of high explosive has been left in a parked Morris Marina on South Carriage Drive, and detonated as the parade passed.

Lieutenant Daly (23) and Trooper Tipper (19) died at the scene.

Lance Corporal Young (19) died the next day and Squadron Quartermaster Corporal Roy Bright (36) died two days after that.

Some 31 other people, including tourists who were watching the parade, were injured.

Speaking outside the court today, Francie Molloy of Sinn Fein welcomed the outcome.

Images of dead horses strewn across the park shocked Britain almost as much as the human casualties. Mr. Downey was identified as a suspect within weeks of the bombing.

The police believe they found a fingerprint match on two car park tickets issued for the vehicle used in the bombing.

But having reviewed the evidence in 1989, the-then Attorney General Patrick Mayhew decided it was insufficient to seek Mr. Downey's extradition from Ireland.

Wanted for questioning over Enniskillen bombing

Court documents also reveal he was wanted for questioning about the 1987 Enniskillen bombing, in which 11 people were killed at a Remembrance Sunday service.

Then came the peace process, the permanent IRA ceasefire, and a deal which permitted those convicted of terrorist offences to be freed from jail.

But the issue of suspects deemed to be on the run, who were wanted for questioning but never convicted, remained in limbo.

The government of Tony Blair tried to find a way of legislating an amnesty. 

The trial at the Old Bailey was due to get under way in January, but Mr. Downey's lawyers attempted to get the case thrown out because of abuse of process.

They produced the letter he had received which appeared to guarantee his freedom.

Peter Hain, the former Secretary of State for Northern Ireland, gave evidence about the delicate nature of the peace process.

He told Mr. Justice Sweeney "I am aware of how critically important it was throughout that most difficult of periods that promises made by and in the name of government must be able to be taken at face value and adhered to".

"The underlying difficulty all had to overcome was the fear that any parties to the process, including the governments concerned, might make false promises or might not be true to their word".

And he said of the arrest and trial of Mr. Downey "I am aware of the level of serious concern and uncertainty that this situation has engendered".

Mr. Downey can go free. In 1987, Danny McNamee was jailed for the Hyde Park bombing, but his conviction was later quashed on appeal.

Now it seems unlikely that anyone else will ever stand trial for the murders.