The families of 34 people murdered in the 1974 Dublin Monaghan bombings announced yesterday they will be going to court to force the government to hand over crucial documents linked to the atrocity.

Forty years ago today three car bombs exploded in Dublin city centre and a fourth in the town of Monaghan. Among the victims was an unborn child, and hundreds were injured.

The bombings, the worst atrocity of the Troubles, were carried out by the loyalist Ulster Volunteer Force, but there have long been suspicions that British security forces were involved. No-one has ever been charged with the bombings.

When the late Justice Henry Barron published the report of his Independent Commission of Inquiry into the bombings in December 2003, he condemned the failure of the British authorities to make original documents available and their refusal to supply other information on national security grounds, saying they limited the scope of his report.

In the years since, strenuous efforts have been made to persuade Britain to release the papers.

Two motions were passed unanimously by Dail Eireann, the Irish Parliament, in 2008 and 2011 respectively, urging Britain to make the undisclosed documents available to an independent, international judicial figure for assessment. Westminster ignored these motions.

More recently, in a meeting with the current British ambassador, campaign group Justice For the Forgotten (JFF) proposed that the documents be assessed in Britain, and even in situ if necessary, so that no issue of national security need arise.

However an arranged follow-up meeting was cancelled by the British side last November and no new meeting has been offered since then.

At a press conference jointly staged by JFF and the Derry-based Pat Finucane Centre this week, they said: “Because of this refusal to continue the conversation, the families feel, after 40 long years, that they can wait no longer.

“They have been very patient. They have decided, very reluctantly, to take the difficult path of civil litigation against the British Ministry of Defence, the Police Service of Northern Ireland, the Northern Ireland Office and the Secretary of State for Northern Ireland.”

The lead cases will be taken in the names of Paddy Askin and Derek Byrne.

Mr Askin’s father, also Paddy, was killed in the bomb explosion in Monaghan. He was 44 years old and left a widow and four small children.

Mr Byrne was critically injured in Dublin by the Parnell Street bomb.

Irish Deputy Prime Minister Eamon Gilmore also this week called for the disclosure of the documents.

Mr Gilmore called on the British government “to allow access on an agreed basis by an independent, international judicial figure to the original documents in their possession relating to the bombings.”