Statistics...
According to the 2019 AEI report on postsecondary attainment, the UK currently has 51.6% postsecondary attainment amongst those then aged 25-34: https://www.aei.org/wp-content/uploads/2019/08/International...
Reports for the entire working-force (e.g. 25-65) will skew much lower due to the significantly lower percentage of postsecondary education in the overall population that started to rise through to the 1990s.
It's disturbingly routine, in the US at least, to have a degree with barely even a grade school understanding of math. And although total illiteracy is uncommon among high-school and college-educated people, you would be surprised how many can't write a normal paragraph or follow a written argument.
You can't necessarily see this with normal public or workplace interactions, but it is real.
I've seen this in myself. In high school, I got up to precalculus level math. I've been trying to relearn it, and when I started, I was amazed that I'd forgotten Algebra 2 level skills.
I don't think this is sufficient as people tend to group with people like themselves. For example, I do not believe I know any adults without a university degree. I might erroneously conclude that virtually everyone goes to university. Most people do not have one.