I have read The Case against Education: Why the Education System Is a Waste of Time and Money by Bryan Caplan. The book is American so not everything is applicable for Britain and I disagree with certain things he says but otherwise there is much truth to his theory that higher education is about signalling more than knowledge.
In bygone years, universities were centres for learning and knowledge rather than qualifications. A degree was required for a few careers such as medicine and dentistry, and it was beneficial for science and engineering, but otherwise university was more about creating intellectual types rather than preparation for the job market. Students studying academic subjects also tended to come from well to do backgrounds or have connections with employers so not many were studying the subject for a piece of paper to get a high paying job from somebody they didn't already know. A significant number of students also wanted to become teachers or lecturers.
I previously mentioned a discussion where it was argued that a degree nowadays is either a financial investment or an expensive hobby as tuition fees has killed the concept of a liberal education by studying for a degree.
One could extend this argument and say that degrees in medicine, dentistry, law, engineering, and certain sciences primarily exist as tools to access these specific careers so they are a financial investment. The situation with arts and humanities degrees is less clear as there are far fewer careers where employers ask for specific arts and humanities degrees. This then raises the question as to whether the value of such degrees in employment is not knowledge but signalling.
What exactly are these dream high-flying graduate jobs?
The truth of the matter is that a career where the job spec asks for any degree; or any degree from a good or Russell Group university; or any degree that is a 1st, does not require a degree in anything. Degrees are not interchangeable between different subjects when it comes to knowledge.
In the case of a career like medicine or engineering where a degree in medicine or engineering is requested then the interviewers will have knowledge of the degree subject in question so they will be able to assess applicants on their knowledge. In the case of a career that asks for any degree then the chances are that the interviewers will not have the knowledge of the degree subjects of the applicants so will be unable to query or assess their knowledge. Therefore a degree is rendered down to pure credentialism and signalling.
Some argue that all degrees provide transferable skills but these are so mysterious and mythical that they probably do not actually exist. It can be confidently argued that basic English and maths, general knowledge, common sense, and soft and social skills are the only true transferable skills. These are not learned at university.