I thought this website might be useful for some of you: www.hmrc.gov.uk/calcs/stc.htm. That said, I tried it and they said I wasn't eligible for a refund on my demonstrating money, which I KNOW I am :|

Having looked at this, we believe that when using this tax checker full time students you should not include their studentship grant in the earnings entry as it is a tax free amount. That may explain why it said your demonstrating money is not eligible.

Having said this, it is dangerous to make assumptions when it comes to the inland revenue so we would recommend contacting them directly for advice.