Relatives of some of those killed in the IRA Hyde Park attack 35 years ago will be marching in central London as part of a campaign to bring an accused bomber to justice.
The organisation UK Veterans - One Voice has invited people to march from Hyde Park Barracks on South Carriage Drive, on Saturday in a bid to bring a private court action against John Downey.
Mr Downey has been accused of the 1982 attack which killed four members of the Royal Household Cavalry on their way to a Changing Of The Guard ceremony.
Thirty one others were injured and seven horses also died in the bomb blast.
The initial case against Mr Downey, from Co Donegal, who has denied involvement, collapsed at the Old Bailey in 2014, when it emerged government officials had sent him a letter in 2007 as part of the controversial On The Runs (OTRs) scheme, telling him he was no longer a wanted man.
Mark Tipper, whose 19-year-old brother died in the blast, wrote on the Hyde Park Justice Campaign funding web page: "We urgently need your help. With it, we can succeed.
"Together, we can ensure justice is done. We cannot allow terrorists to get away with murder."
He added: "We need to hit our fundraising goal before August 1st otherwise we will lose our chance and the chief suspect will evade justice yet again."
Mr Tipper also blamed former Labour prime minister Tony Blair for a ''shameful and secret deal'' which allowed suspected IRA members to walk free.
''The chief suspect walked free from the Old Bailey because of a shameful and secret deal by Tony Blair with the IRA", he said.
''Because of this we have been forced to take our own private legal action.''
The families of the British soldiers killed in the bombings were left furious after discovering Mr Downey received £50,000 in legal aid, while their own application for legal funding had been denied.
With the Legal Aid Agency refusing ''again and again'' to fund the case, Mr Tipper added: ''We have been made victims three times over.
''First by the bomb, then by Blair and now by the bureaucrats of the Legal Aid Agency.'
Relatives of some of those killed marked the 35-year anniversary of the atrocity in Hyde Park on Thursday as more than 100 Household Cavalry veterans turned out in support.