It's interesting what is now regarded as middle class. I think that the richer and more educated section of the traditional working class seems to have been revised upwards? Nurses and office workers... My father is from a traditional WC family: growing up on a council estate, his father was often unemployed but worked in the payroll at a factory and his mother worked in an office typing letters. All but one of their dozen children went to grammar school, incidentally, and if you met any of them you'd think they were working class, and they are! They are also literate and creative people, with strong interests in art, music, engineering, and political debate. Those things are obviously traditions of the working class as evidenced by Artisans Libraries and Mechanics Institutes all over the shop.
My mother's family is what I (had previously) envision(ed) as middle class and they were mainly lawyers, soldiers, diplomats, younger sons of younger sons and other people clinging on with a death grip to the bottom rung of the aristocracy. People who work, but do not struggle. Or, well, no I spose some of them don't have to work as they have trusts but they're not upper class - the trusts are from businesses liquidated in the 19th century and other trading sources. They're Isobel and Matthew Crawley, not Lord Grantham.
What neither of the families have is much of this peculiar anxiety about authenticity, which probably means none of them are truly middle class. I can't imagine any of them having strong opinions on towels. Olives and towels and so on are very Molieresque, aren't they?
Anyway, actually I think meaningful class divisions are broadly determined by power and access. Probably you could determine it by assets and connections, with connections (or social power) having the edge over financials in some respects. Or to put it bluntly: there are workers and there are owners, and all the rest is the narcissism of small differences.