I agree. I have two kids at uni and I earn less than £18,000 PA. My kids both get a bursary of £500 / year. They also get a loan but it’s not even enough to pay the fees for halls ( self catering in an inexpensive city outside the south east ) .
One has a part time job but the other has additional needs so can’t cope with a job on top of course work.
So no, you don’t have to be a top earner to have to support your kids through university.
Yes I was married and financially secure - until he ran off with his mistress taking our savings with him.
And yes I did work outside the home, all through my marriage, but my career and pension were badly affected by having to go PT to care for my SN child and of course doing all the housework and child care to support my husband’s career and his working evenings and weekends ( which turned out to be shagging other women ).
And yes I did apply to the child maintenance service for child support but my ex quit his job, went “ self employed “ and suddenly went from earning a six figure salary to earning practically nothing ( after he’s put all his profits into his pension and paid his shareholders of course ). Last year I got £14 for one child and the year before I got £92 for two. That’s per year, not per week ).
So my advice to the OP is don’t have a 4th child unless you personally can earn enough to support all 4 children yourself . Because it’s very easy for men to leave and do nothing for their kids and pay nothing. No one thinks it will happen to them. Everyone’s marriage is secure until it’s not 😢