Actually I used to work as a make-up artist and you don't need to go to an expensive school if you want to work in fashion, none of the people I worked with or aspired to work with went to beauty school. The best education I got was from other make-up artists who were working on the types of jobs I wanted to do. You don't need a degree, nobody cares! It's all about what you can do, the only exception I ever came across was that I couldn't work in salons because I didn't have an aestheticians license (but who cares the pay sucks in salon jobs). This could be different in the UK but I doubt it (a few artists I worked under reguraly worked London fashion week and they have nothing more than high school diplomas).
Best thing I could say is invest your money instead in a few good books (the 3 by Kevin Aucoin are the best ever) and just practice the techniques. Considering you live in London (I'm jealous) it shouldn't be hard to find some great make-up artists who you could talk to and hell ask about apprenticing - that would be the best way of getting into the biz. There are some agencies that specialize in representing make-up artists, stylists, etc. Find them and go ask the're advice too (they could also maybe hook you up with pros).
Good Luck, it's hard work but totally more than worth it. I hope that helped you a bit.
P.S. Confidence, persistence, and a thick skin are the things you need to stay alive in fashion. If you have those it's not scary and you'll make it.