Comment by ajb

U.S.S.R. military had far more complete maps of many parts of the U.K. than Ordnance Survey published.

Although amusing, note that its than the Ordnance Survey published. I.E. they had the data, it was just classified. Also, it's fairly clear that the Soviet maps were mostly derived from OS maps. Looking at my street, for example, they have it in a pre-WWII configuration which they could only have got by starting from a rather old OS map. So they clearly only checked for differences in areas they thought important, such as government or military areas - they didn't have people mapping the whole UK. Still it's probably true that one can get more information about certain areas in these Soviet maps than in extant OS maps.