@AlisonMiranda Here you go:
Over 18 but no financial support
If an adult child finds themselves aged 18 but without any financial support for university, there is provision.
Under the Schedule 1 Children Act 1989,
an adult child, in education, can make an application for maintenance (periodical payments) from one or both parents.
The application cannot be made if the parents are still living together in the same household, but only if there was no maintenance order in force with respect to him/her before immediately before their 16th birthday.
Such applications these days are rare predominately because of the availability of student loans to pay for both tuition and living costs, but also that an adult child is unlikely to get legal aid to fund their application.
The provisions for adult children after the age of 18 can be complex and so it is always better for the parents to agree on how they are going to support their children through university and until what stage.
Realistically, the paying parent would be poorly advised to agree post A-level maintenance paid to the other parent because they could not guarantee it would reach the intended recipient. I was very clear with my ex-wife that I would support my children at university but it was a matter between me and the children, not her.