The official history of MI5 by Christopher Andrew tells us that when direct rule began in Northern Ireland in 1972, the post of Director and Co-ordinator of intelligence was offered to MI6 because nobody senior enough was available in MI5, and that MI6 took the lead during this period because, as a foreign intelligence service, it was more used to operating on 'hostile territory'.
As David Charters has noted, this explanation seems curious given that MI5 had provided the directors of intelligence at the Army's HQ Northern Ireland between 1969 and 1972. Indeed, Andrew ignores this position entirely, which is perhaps a commentary in itself on MI5's role in the military escalation of this period.
This, however, is one of several areas where researchers who worked on Andrew's book have produced accounts which expand on the official narrative. Calder Walton's Empire of Secrets is one example of this genre. On Ireland, Tony Craig's work on the relationship between security and political intelligence is particularly important.
Previous scholarly literature, such as Andrew's Defence of the Realm and Philip H.J. Davies' MI6 and the Machinery of Spying has tended to portray the relationship between MI5 and MI6 in Northern Ireland as a collegiate one. This was presumably the intention when the Irish Joint Section was formed to bring together MI5 and MI6 agent running in 1972.
However, from the 1970s onwards, investigative journalists, influenced by whistleblowers such as Colin Wallace and Fred Holroyd, have presented the MI5/6 relationship in Ireland one of intense rivalry. Post-Troubles inquiries have revealed significant evidence to support that interpretation.
Craig's concept of a 'security stovepipe' may help to put that evidence in some perspective, and provide a useful tool for analysing the intelligence dimension of the whole history of the Troubles.
Ironically, the best evidence for a collegiate relationship between MI5 and MI6 comes from the end of the conflict. This was the link forged, not in Ireland but in a Middle East counter-terrorism joint section, between Michael Oatley of MI6 and John Deverell of MI5, two key players in the covert back-channel to the IRA that helped to launch the peace process.