Former garda whistleblower John Wilson is among those accompanying a group of Irish people travelling to London today to seek justice for their relatives who died violently.
The trip is part of an international campaign about cases of alleged garda malpractice and state cover-up.
The families have already travelled to the European Parliament, where Irish MEPs expressed their solidarity and wrote to the Minister for Justice voicing their concern.
Among those who will meet MPs in Westminster today is the mother of Shane O'Farrell, who was killed in 2011 by a hit-and-run driver, and the twin sister of Mary Boyle, the six-year-old girl abducted and murdered in Donegal in 1977.
Ex-garda whistleblower John Wilson (pictured), who is travelling with the group, has accused the Department of Justice of turning a blind eye to evidence of wrongdoing and corruption.
"These people are desperate," he said. "They have suffered years of psychological torture in not getting the answers that they require in order to finally enable their loved ones to rest in peace.
"These people really feel they are not going to get justice from the Irish authorities and the Irish State. This is very, very sad.
"It is a damning indictment of the Irish justice system that these people have been forced to travel outside the country seeking assistance from British parliamentarians."