Technically, by the old social scale, Cameron would be considered upper middle while his missus is upper class, being born to titled parents and having a family seat! Upper middle class, like Cameron and Johnson, does tend to be a bit more exaggerated; have a listen to recordings of upper class Diana Spencer and compare. Upper middle and above does public school, lower middle does private or grammar if they can afford it, the middle middle do public or private depending on funds, and the rest of us muddle along with state!
The posher you are, the less you buy things like furniture (or even clothes) as you inherit it. Millionaire Heseltine was damned at the posher end of the Tory Party as 'the sort of man who had to buy his own furniture' so all Jack's Shack contents don't give her any more social standing. When I was growing up, the local posho, an earl, wore paint stained overalls as he DIYed the family castle restoration....