Brevet is no assurance them civvie types will know what you do! Got stopped by a salesman at a motorway service station whilst in 1's trying to sell me some piece of tat or other. Came to the end of the conversation and he asked "so what is it you do then?" and genuinely had no idea I was in the military at all....
As for not shopping at harrods, family instructed (not a drama as mrs target already a f&ms hamper kinda gal)