Here is a good class-test you can try: when talking to an English person, deliberately say something too quietly for them to hear you properly. A lower-middle or middle-middle person will say 'Pardon?'; an upper-middle will say 'Sorry?' (or perhaps 'Sorry - what?' or 'What - sorry?'); but an upper-class and a working-class person will both just say 'What?' The working-class person may drop the 't' - 'Wha'?' - but this will be the only difference. Soem upper-working-class people with middle-class aspirations might say 'pardon', in a misguided attempt to sound 'posh'.