I don't see a problem. If rich foreign students can pay to get themselves on to a course at a university, why shouldn't British students be able to do the same?
Either you stop everybody (British or foreign) paying to get themselves on the course or you allow everybody. Otherwise you are discriminating against British students.
I don't like the idea that anybody can pay to get themselves on a course. I'd prefer it to be purely on ability. However, given that I'm told the "edueconomy" is so important to the UK, then if universities are going to want to offer courses to affluent foreigners then affluent British students might aswell be allowed the same opportunity.