I think as well, the middle class tend to make more of a song and dance about it. The upper class know their position in their world and they're secure in it, while the middle class (obviously not all of them, just the general "type" we're talking about) are more insecure and more desperate to show everyone "look! Look at me! I am doing well for myself!" So it's the middle class who say things like "oh darling you know I only buy designer, I wouldn't dream of having anything other than a Smeg", who change their accents to sound "posh" and who try and show off their wealth more to prove they have it. In my (limited) experience the upper class don't feel the need to do this
The thing is, as well, there are sliding scales within the three basic classes.
The upper class goes from dukes to baronets with history influencing it too; at the top among the dukes, you have the ancient Norfolks against the hugely rich but more recent Grosvenors, and you have all the Edwardian up-from-trade ones too. A lot of them would have considered Diana posher than Charles... The working class goes from the skilled trades, through respectable but manual/retail workers, until you get down to the almost feral underclass,
Shameless style. The middle class has all those gradations too, from the likes of Cameron and Johnson to police/nurses/firefighters/etc.
Money has nothing to do with it. When I was in the reserves I knew someone who had a title but no money other than what he earned as a local government officer; he's now an earl but not really any more wealthy, all the family holdings having been handed over to the National Trust, and lives in a bog standard house. As you said, the middle class are the least secure and always trying to hustle their way up but it's less to do with money than attitude, habits, behaviour, standards, etc. All the things that Jack and her family own don't make a difference until they start sending their children to public schools to mix with the Johnsons et al (and don't forget that Osborne
only went to St Paul's among that crowd), take on the often shabby trappings of the upper middle or get given a hereditary title. She's simply not in the same crowd as the upper middle Lawsons nor has she the ability to mix with the more successful arty and showbiz Groucho/Soho House crowd.