In times gone by, when we had to wear civvies on RAF trooping flights in case of en-route diversion there was a reason. For example, our French 'friends' didn't permit military overflights so AscotXXX masqueraded as a civlian flight. A UK airport and domestic flights etc. don't come anywhere near the unwelcome diversion rule. Its home, its our country and our military. I'm pleased, not to say proud to see servicemen out and about in uniform and I'm sure that the majority of people are too.
In any case, is it actually legal for servicemen to be out and about in disguise?