so i think it's common in fics for mi6 to have a lot of top secret information only stored on paper for opsec. which i understand, but the problem with paper is that it takes up a huge amount of space, is difficult to search through quickly, is very flammable/easy to damage, difficult and time consuming to duplicate without digitising (when needed) and is also very vulnerable to insider espionage which can go undetected for a while (if detected at all)
how do you fix this issue? well the common thing to do for many archives and libraries when storing lots of paper data (such as newspapers, maps, etc) is microfilms like microfiche, but i want to suggest:
the humble floppy disc!
it is relatively space efficient, allows you to collate and search data more quickly (stores small databases as well as old software etc.) it's a pretty efficient way of storing data digitally without the risks of HD-based storage!!
q/q-branch can then lock up the discs in archives with controlled access, and limit access to the computers in six that can read them, as well as not connect those computers to the internet. this makes it harder for internal espionage/double agents to access the data without it being very burdensome to keep track of the movements of every person who enters archival stacks. the clear cases and colourful nature of floppies, combined with limited number of computers to access, makes it easy for archivists to spot swaps. it also makes it easier for archivists to fetch relevant discs (and be in charge of loading/unloading them into computers) for those who need them, again without taking a huge amount of time like paper documents would.
if someone does manage to steal a disc, it's easier to track who has done it, because purchases of computers that can read a floppy would be obvious, or harder to hide in a home (if they manage to purchase it untracably/still had one that worked/etc).
moreover, it stands to reason that mi6 may have begun a digitisation project in the 70s, when floppies and computers first started getting commonplace and cheap enough for 6 to justify purchasing a larger volume of them. changing the format of data storage is a very difficult and expensive project, and data loses some of its integrity as it's converted. so, if it ain't broke!
i think it's a good solution for restricting access to a lot of top secret data that can be stored on them (like personnel data), that uses existing formats and protocols, rather than inventing something wholecloth and having to fence it off etc.