The “McGimpsey case” that challenged the legality of the Anglo-Irish Agreement concerned the British government in 1987, declassified files reveal.

In particular, there was high-level concern in the Northern Ireland Office (NIO) that a verdict ruling the agreement unconstitutional would undermine the Irish government’s support for it.

The case at the Dublin High Court was taken by the brothers Chris and Michael McGimpsey, both Ulster Unionists and company directors from Co Down. Michael later served as health minister in the Northern Ireland Executive.

In their submission, they argued that the Irish government’s signing of the agreement was unconstitutional because it was repugnant to articles two and three of the Constitution, which articulated the extraterritorial claim to the North.

In a detailed memo on the subject, entitled “The Agreement and the Irish Constitution: the McGimpsey Challenge”, circulated to officials on July 10th, 1987, PN Bell of the NIO dealt with the significance of the challenge for the British government. In his view, “the least desirable outcome” from the British viewpoint, would be a finding of incompatibility between articles two and three and article one of the agreement.

Bell felt the case meant the Irish government under Charles Haughey would be called upon to make its position plain: "This will present political difficulties for Mr Haughey, who has said he has reservations about the constitutionality of the agreement, although he has agreed that he is bound by i."

The official believed Haughey would wish to “avoid a crisis in Anglo-Irish relations”.

Bell concluded that the Irish would be wary of discussing the case with British ministers as it went to “the raison d’etre of their State”.

In the end, the High Court ruled against the McGimpseys.