John Downey, 68, is accused of murdering the soldiers.

But a 2014 prosecution against him was dropped after a judge ruled that an official letter telling him he was no longer a wanted man given in error meant he could not face trial.

The letter assured him he would not be arrested and prosecuted for IRA crimes.

Then Prime Minister, David Cameron, said it was a “dreadful mistake”.

Squadron Quartermaster Corporal Roy Bright, Lieutenant Anthony Daly, Trooper Simon Tipper and Lance Corporal Jeffrey Young were all killed in the attack on 20 July 1982.

Now the Legal Aid Agency has confirmed it will fund the families’ case.

Danny Kinahan, former Ulster Uninioist MP, welcomed the news.

He said: “The granting of legal aid to the Hyde Park Justice Campaign is fantastic news, but it should have happened a lot sooner.

“The families of my murdered colleagues have been put through hell.

“Firstly, they lost their loved ones, stolen from them in the prime of their lives.

“Then, they suffered the pain of the farce of the trial of John Downey being thrown out because of one of the despicable on-the-run letters.

One other man was convicted in relation to the death but was later acquitted on appeal.

Photo credit: By Source (WP:NFCC#4), Fair use.