The report found the police investigation following the January 1976 killings failed to arrest and interview 11 men identified by intelligence, with the failures described as taking place against ‘wholly insufficient’ resources.

Ten workmen were shot dead by the IRA in the attack, with only Alan Black surviving the shooting. The only Catholic among the group was identified and told to leave the scene before the killing began. No one was ever charged with the killings.

“The Kingsmills massacre was one of the most nakedly sectarian acts of the entire Troubles, in a time period filled with such incidents,” said Lagan Valley MP Ms Eastwood.

“The families of those killed have long campaigned for justice for their loved ones, and particular praise goes to Alan Black for his unbelievable strength and pursuit of the truth in the nearly 50 years since the murders. He has also rightly hit out at the length of time it has taken to produce this report.

“Clearly he and the families feel let down as they come to terms with the findings of today’s report. This further reinforces the need for a fully comprehensive and victim-centred process for dealing with the past, so victims, survivors and their loved ones can receive the truth and justice they deserve.”