I thought you HAD to do your A-levels before university in the UK. You have to get an A-levels equivalent if you want to go to university (college) in the US. I had to take them.
Your work is great by the way Phil. I almost wish I were 17 with your skills. But like Chili said, if you get the chance to go to school, I'd go. It doesn't matter WHAT you major in. No teacher will be able to teach you what you learn on your own. You might as well learn writing or psychology or something so you can write something cool.
I'll give you an example. I don't know if this story is true, but I worked with a guy who told me he went to school with Chris Nolan's brother. He said that his brother got the idea for Memento when a Psych prof told them something like "imagine that you only had short term memory, which had no relation to long term memory, write what your life would be like." That gave birth to Memento, and Christopher Nolan made that movie his brother wrote. My colleague was telling me (this is 2004) how this guy was now hired for 400 grand to write "anything" and 'they' paid for his hotel to stay in LA for 6 months. I didn't check at the time if it were true, I was too busy, but I was just checking out IMDB and it seems that it very well could be.
So go to school and major in something other than film. Do film on your own time (for your classes even), which there will be plenty of in school.
Cheers,
Aveek