.... 11 Marlborough St, in Bath, Somerset.
I have no idea if you are still active on these forums Ayashi, as I note your post I have quoted dates back over 7 years, but...
My Grandfather was also a civil servant employed by the MOD, specifically the Royal Navy. He spent time as an enlisted man at the outbreak of WW2 but was then mysteriously released to become a "civil servant". It was during this period of the war that he married my Grandmother and my mother was born. We know that he never talked about his work, even with my Grandmother, they went on to divorce just after the war finished. We know that before the war he was amongst other things listed as a "radio engineer". His marriage certificate to my Grandmother has him recorded as an "Electrical H.F. Engineer", for my Uncle's birth certificate he is a "Admiralty Radar Worker (H.F. Engineer Wireless Firm)".
My Grandfather then spends his entire working life in secret, he marries again and goes on to have children with his second wife. He ends up retiring as a "Senior Scientific Officer - MOD - Navy", that's what his death certificate says.
My Grandfather was a whizz with electronics of the day by all accounts and was a keen ham radio enthusiast. Purely by luck, another enthusiast asked me what his Ham radio call sign was, I gave it to him and the most astonishing thing happened, we were able to find which address he lived at from 1947 right up until his death. The radio directory for call signs was published each year and we have a complete history of where he lived. We have corroborated these addresses with birth and marriage certificates from his second family.
Interestingly, from 1961/62 until 1973/4 he lived at 11 Marlborough Lane, Bath. Now I realise your great Grandfather was at 11 Marlborough Street, not Lane, but I felt I had to post!
Did you manage to find anything more out? My hunt so far is pointing to MOD Fox Hill or MOD Ensleigh.