British Orienteering has an archive in the Special Collections department of the Sheffield University Library, containing a large quantity of paper records of all kinds going back to the very start of orienteering in the UK.
These include maps and results files from almost all registered events held from the late 1960’s until early 2009, and all British Orienteering Federation Council and Committee records up to the time of digitalisation. Complete sets of all national o-magazines including The Orienteer, CompassSport and Focus, and most regional magazines from their first issues until some point in the 1990’s are in the archive. There is an extensive collection of books, including almost all books about orienteering ever published in the U.K.
And much else besides! An outline description of the collection can be found here, and the full archive listing and the Book List can be downloaded as pdf files.
Visits to the Special Collections department can be made by appointment; the reading room is open from 9:30 am to 1:00 pm and from 2:00 pm to 4:30 pm on most weekdays. It is best to decide in advance what you want to look at, and the relevant boxes will be brought into the reading room before you arrive. Additional items can usually be brought out at short notice.
Contact and location information can be found here.