The one where the GCHQ operate in Cheltenham is apparently where all the top secret stuff happens. The building looks quite stylish also, donut shaped.

A few years back Sky News got "exclusive" access to the base. I cannot for the life of me find the story but I'm pretty sure I didn't imagine it.

I can say the BAE facilty in Brough seems very suspicious to me. Intruder detection systems all around its boundaries. Its massive, seems to have an underground element. Very security conscious. It seems very sort of clean and unused, for a massive fully operational factory. Indeed they used to make military craft there but dang, it just has that air of suspiciousness. I and others have seen many strange lights in the sky near it, capable of amazing speed and control that seems beyond conventional tech.