Relatives of the Birmingham pub bombs - for which six men including John Walker from Derry were wrongly convicted - are demanding that the British Government release secret files which may hold vital clues.
Campaigners for victims of the bombings will meet British Home Secretary Theresa May this week to press for a new inquest into the deaths.
Bereaved relatives will also challenge the British government on claims a disclosure embargo on confidential state files related to the 1974 attacks has been extended to 75 years.
Twenty-one people were killed and 182 injured when the suspected IRA bombs exploded in two city centre pubs on November 21, 1974.
The six men wrongly convicted of the murders – the Birmingham Six – were released in 1991 after their convictions were overturned by the Court of Appeal amid evidence of police fabrication and suppression of evidence.
They were Hugh Callaghan, Patrick Joseph Hill, Gerard Hunter, Richard McIlkenny, William Power and John Walker.
An inquest opened days after the bombings was closed without hearing evidence in 1975 in response to the guilty verdicts.
Campaign group Justice 4 the 21, which represents relatives of a number of the victims, are calling for a new inquest to be ordered. An application requesting a fresh probe has been lodged with Attorney General Jeremy Wright.
Relatives will ask for the support of Mrs May and Northern Ireland Secretary Theresa Villiers at a meeting at the Home Office in London.
Julie Hambleton, whose 18-year-old sister Maxine was killed, said the 21 victims had a right to a proper inquest.
In relation to the release of state files, Ms Hambleton added: “If they have got nothing to hide why have they buried the evidence for 75 years?”
The campaign group is being assisted by Belfast-based solicitor Kevin Winters.
From 1975, the Birmingham Six struggled for justice after their wrongful conviction, until their second full appeal, in 1991, was allowed.
Hunter was represented by Lord Gifford QC, others by human rights solicitor Gareth Peirce. New evidence of police fabrication and suppression of evidence, the successful attacks on both the confessions and the 1975 forensic evidence caused the Crown to decide not to resist the appeals. The Court of Appeal, constituted by Lord Justices Lloyd, Mustill and Farquharson, stated of the forensic evidence that “Dr. Skuse’s conclusion was wrong, and demonstrably wrong, judged even by the state of forensic science in 1974.” In 2001, a decade after their release, the six men were awarded compensation ranging from £840,000 to £1.2 million.