"I beg your pardon" is regarded as 'middle class' when it's used as a substitute for "What did you say?" (or, simply, "What?").
Members of the 'upper classes' would definitely 'look down their noses' at anyone who used it, preferring something like "I'm sorry, I didn't quite catch what you said" (or, as Prince Philip would simply say, "What?").
I often hear people say 'yer what' nowadays instead of 'pardon'? Or as an apology "Sorry" instead of 'I beg your pardon'. Only as a precursor to a row in a Miss Haversham voice, have I heard "I beg your pardon".