This link below is to the ANO - Article 101 is the relevant piece of legislation
http://www.caa.co.uk/docs/33/CAP393.pdf Evo7 got it just about right, I think. Basically, you can't do PPL, aircraft rating or Night rating training or tests. You need the CFI's permission to take one of my club aeroplanes to an unlicensed field and I think the Insurance excess is doubled.