I don't think class matters at all and I think for the most part all classes mix well. I'm bog Irish working class and my Mrs was upper class, no problems at all, class is all in everyone's heads.
I think the traditional UK class system and attitudes are pretty much dead now (thankfully). a person from a "lower class" background can easily achieve more in their life with hard work than a lazy person from an "upper class" background ever will.
You really need to ask me? Good heavens, my old chap!Never gave it a thought.
I suppose one distinguishing feature of the middle class is that they worry about class. The working class and the aristocracy and upper class neither bother nor have to. They know their place.