Despite the BT Tower being one of most recognisable and conspicuous buildings in London, it was classed as an official secret until fairly recently, and taking or possessing photos of the BT/Post Office Tower was technically an offence under the Official Secrets Act. In line with its 'secret' status, this 620ft London landmark was also omitted from all Ordnance Survey maps until the mid 1990s.
Kate Hoey MP, speaking in Parliament in Feb 1993: "Hon. Members have given examples of seemingly trivial information that remains officially secret. An example that has not been mentioned, but which is so trivial that it is worth mentioning, is the absence of the British Telecom tower from Ordnance Survey maps. I hope that I am covered by parliamentary privilege when I reveal that the British Telecom tower does exist and that its address is 60 Cleveland Street, London"