The constitutional implications of MPs from Northern Ireland voting on "purely domestic matters" in the House of Commons was raised as a matter of urgency in 1967 by the British prime minister, Mr Harold Wilson.
In February 1967 Mr Wilson sent a secret note to the lord president of the council and leader of the House, Mr Richard Crossman, warning him that "no hint of this matter should be allowed to reach Ulster ears!"
Mr Wilson said he had raised the matter in 1966, that Northern MPs should not have the right to vote on domestic matters, "where Stormont has exclusive jurisdiction on the same subject".
While "Northern Irish MPs could have voted the government out of office" on naming the UK Iron and Steel Corporation, Mr Wilson wrote, the attorney general had produced "a very serious study . . . with weighty arguments against any change".
In May Mr Wilson noted that the Northern Ireland prime minister, Capt Terence O'Neill, agreed that the number of Northern Ireland MPs should be reduced to "off-set" the fact that they would be consulted on matters which did not directly concern Northern Ireland. Mr Wilson wrote in his personal minutes that the in-and-out principle, whereby a larger number of Northern MPs would be allowed to vote on a limited number of issues, was "considered and rejected".