I think Slothrop has it spot on in the first post, in that the concept of middle-class-ness is very much a middle-class obsession. Even more explicitly: if you've ever started a thread on an internet forum titled "What is middle class?", you're probably it.
I don't think it's a useful term any more. It was useful in the 19th century when Marx and Engels were writing, and in European and especially British society there were several well-defined social strata that were more or less defined by what you (or your husband, or your father) did for a living: toffs who simply owned land, a working class who did manual labour of some variety and a middle class in the middle, who did jobs that you'd had to have been to a good school and then probably university to do. And obviously an underclass who had no legally or socially acceptable job at all (thieves/beggars/whores). Whereas these days you have people with PhDs from top universities who can't get a job, or are doing a job that could be done by more or less anyone with a reasonable grasp of English and a working knowledge of Microsoft Office, and people my brother, who left education at 18/19 and are doing very well because of skills they can use in emergent industries. So (unlike in America, I think) straightforward economic position or job type is no longer a good indicator of social 'class'. Which leaves tastes, attitudes and all the other rather woolly social things, which are problematic because if you use these to define who is (and isn't) middle class you end up implying that someone is disqualified from being working class if they drink red wine, eat olives and read
The Guardian, even if they happen to be a bus driver descended from a long line of bus drivers. In fact it's tantamount to implying that working-class people are by definition uneducated and uncultured.
I'm reminded of something my girlfriend told me, which is that a couple of months back she was having a half of bitter in the 'spoons in Stansted Airport while waiting for her plane, and there was a group of loud, bleach-blonde women sharing a couple of bottles of rosé around the next table, all wearing matching T-shirts, probably off for a hen do somewhere in the Med; and that their respective choice of drinks was pretty much a class inverse of what it would have been a couple of generations ago.
chavs 'take holidays' the middle class spend summers at X
Oi, I just took a holiday! You calling me a chav? I'll fuckin av ya, ya cunt.