History has shown that intelligence can be ineffective or misunderstood without proper collation and organisation. Hence, administration and record keeping form the nucleus of an intelligence organisation. Recent studies of intelligence debacles, such as the failure to prevent the 9/11 terrorist attacks, have revealed the terrible consequences that can result from a nucleus divided.

MI5’s own nucleus was its Registry (which ran the file and indexing system). Devised in the immediate pre-First World War period, it did not fundamentally change in peacetime. Even after the Registry overloaded MI5 in June 1940, virtually collapsing, Sir David Petrie, who was about to become the DG of MI5, concluded that B Division merely needed ‘manipulation rather than surgery’. It remained fundamentally intact.

The basic organisational structure consisted of file groups. The ‘Personal File’ (PF) formed the central pillar of the system. One PF per suspect included all reports on that individual, including press clippings in which the suspect’s name appeared. Those reports that did not fit neatly into a PF were mostly filed in the place-card index. Known as Official Files (OF), these documents related to certain government departments or offices. Any remaining files not classified as PF or OF were indexed as Subject Files (SF). Although these miscellaneous subject files constituted the dregs of intelligence before the war, their usefulness grew over time. The importance of the OFs, by contrast, waned. All of the names and subjects contained in the files were further cross-referenced in a general card index so that ‘particulars regarding the association of any of the names with other given names, places, or subjects could be quickly traced when required with any enquiry’. Covers added to files shortly after the beginning of the First World War, creating space for noting a file’s contents, its usage, and notes made by different branches.

Not only were targets, whether individuals or organisations, therefore made part of a web, so was the investigation process within MI5, important because ‘experience showed that not only in the filiation of cases, but also as a means of obtaining proof against agents, their “contacts” were of immense value’.