In reply to Trangia:
> I found it a fascinating documentary, particularly the fact that the USSR had detailed maps of all our military installations which had been left off the OS maps for security reasons! As the commentator said, all the Soviets had to do was buy our OS maps and look for the blanks on them, before filling them in from satellite surveillance.
old-maps.co.uk has soviet maps from the 1980s available. Comparing them to the OS maps is interesting. For example, Chatham dockyard is shown in detail on both the OS 1:10,560 plan of 1967-1970 and the OS 1:10,000 plan of 1970-1976. If the soviets had got hold of that latter map (which I don't think would have been all that difficult - AFAIK six-inch maps were readily available, albeit at a price, for people like surveyors and town planners to use) then that would have given them a very useful starting point for their own 1:10,000 map, to which they could add changes observed by satellite surveillance and, as Rob Naylor pointed out, useful information collected by "boots on the ground".
On the other hand, Chatham Dockyard is definitely missing from the 1961-1962 1:10,560 OS map (and the 1898 one, in fact). I suppose it's possible that old-maps.co.uk have access to fully digital versions of the more recent OS Maps which aren't redacted. (I can't remember when the programme said that the OS started digitising their maps but I imagine it would have been around the late 60s/early 70s.) Older OS Maps on that site are, I believe, based on high resolution photographs/scans of printed map sheets.
Looking at the maps on the National Library of Scotland site
http://maps.nls.uk/index.html - which definitely
are scans of printed maps - the dockyard does appear in detail on the six-inch OS maps on the 1930s. So it looks as if it came and went over time, possibly re-appearing even during the cold war.
Post edited at 08:35