Well, you can look at me as to the reason why.
I work as a Biochemistry professor predominantly, but I do mooch around government laboratories and ex-government privatised research facilities almost every week. My position at these facilities even comes with a senior army rank because of the type of facilities involved - I passed Lieutenant Colonel last year. For this advisory work, you could call me a civil servant. However, you can bet your bottom dollar that I can't and won't reveal the nature of my job in this capacity.
There's a lot of us about and this is why if you take a look at the newspaper honours lists, you'll often see entries such as "Joe Bloggs, Grade 6, MOD" amongst the lists of gongs awarded. Some of these guys keep this country safe big time, believe me and need the job anonymity. Plus, never forget that the Official Secrets Act is an omnipotent and very powerful persuader.