I'd agree that you can get a lot out of online writing groups and forums like AbsoluteWrite.com, and they don't cost anything. If your budget is limited, save your £500 until you have learnt everything you can from all the free resources, and a few inexpensive creative writing books, and then you will be in a position to make an informed choice about how to spend the money, whether on writing lessons or a conference or a paid critique.
I would recommend online writing groups more than courses. You can learn structure from a book - but you need to workshop prose. Or check out a writer you admire. Sometimes newer writers - but one who produce good work - have such courses.
Hi, I did a creative writing course about 10 years ago and I learned a little. However I've learned far more by reading AbsoluteWrite.com and contributing there. Lots of great experience. I also set up my own writers' group where we're all beginners but encourage each other.
Have you written much yet? If so, you may feel a course would be right for you, but if not, I'd recommend writing a lot first, reading/contriibuting on writing forum and then choosing to spend your money on writers' conferences or suchlike.