Anyway back to answering Firepants. Thanks for the compliments
I'd strongly advise joining a life drawing class or we are unlikely to accept you. Life drawing does not have to be expensive though, join the
http://london-life-drawing-society.ning.com/ and you should be able to find your local group and most are very reasonable. Sketches of family members can be god (if done well enough) but we need to know whether you really understand anatomy, and you're only going to get that with life drawing. Digital painting is something we like, but not essential - as long as you have traditional painting skills that will be fine (we'll teach the digital painting). You should have images that show knowledge of perspective (two point or higher), colour theory and composition. I don't care what you draw/paint them in, as long as you are demonstrating those skills. Yes you can include work from your A-level as long as it's good
If you are having to do nothing but copy Salvador Dali or Monet, well don't bother putting that in, or at the other end, if you are having to make a load of conceptual crap, leave that out as well. Look at the work and ask yourself - does this show talent? does this show ability to record the world outside yourself (or inside if it comes to that), does it show technical skill and creative design? Don't worry about a portfolio telling a story - although that is a good piece of advice if you are applying for a fine art course. Having images, each one that tells a story is a damn good idea, especially when making concepts for characters or environments. But we wouldn't expect that to extend through an entire portfolio.
Regarding 3D yes we want to see it, we prefer to see work you've made yourself rather than tutorials because most (decent) tutorials also come with the files so we don't know if you just used those, plus it shows zero creativity on your part - and you do want to demonstrate creativity or there's no point in becoming an animator
Screen captures of models are great. Show them from different angles.
I don't know what other universities will want, but a MOV with h264 codec or MP4 file are the industry standards for compressed file delivery and that's what we like too
Don't forget to compress the sound as well - ALaw or IMA 4:1 are good audio codecs.
Hope that helps