From my experience living most of my life in the UK from birth there is an element of truth to class being immutable - being directly linked to money and the status of property ownership - for now anyway.
The Thatcher years created an opportunity for working class (who traditionally lived in rent controlled properties due to low income) to purchase their houses for pennies on the dollar.
Suddenly, millions of families felt they had moved up a class. They were no longer at the mercy of landlords and had moved up in society from a tenant to an owner.
The traditional three tiers of lower, middle and upper class changed to lower, lower-middle, upper-middle and upper.
From my observations the lower-middle class are still adjusting not to having money but rather _access_ to money previously denied. Having equity in a property as a guarantee of a loan opens up a world previously off limits by the banks.
A bit like when someone turns 18 and they have access to credit cards - lots of cash easily available!
I come from a family where (with the exception of a mortgage), if you can't pay for something in cash (and still have plenty in reserve), you can't afford it. My folks were very proud of raising a family with zero debts (minus the mortgage), and I'm forever thankful.
The families I knew (and by extension others living on the typical "cookie cutter" UK housing estate) were swimming in debt. What surprised me the most was how "normal" it was - 3yr (or less) car on the drive; massive flatscreen TVs (in 2007); multiple cruise holidays per year; flying off to a warm destination mid-winter.
Many of them said when they were younger they never experienced such things and told stories of growing up in near poverty. Going into debt for holidays and having a new car on the drive was normalised.
These were nurses, postmen, truck drivers, retail staff, hospitality etc. all traditional working class jobs with low salary expectations.
They were trying desperately to _appear_ like they were middle class at whatever cost.
I'm of the belief it will still take a few generations before the wave of lower-middle class learn that it's not about having a new car on the drive but rather having that cash in the bank as savings - and a significantly cheaper (& older) car on the drive.
And yet the UK school system doesn't teach pupils about sensible financial matters - we all rely on our parents to guide us - so escaping the "buy it now on credit" mentality will be easier said that done!