ambernought, Sorry to put a downer on it, but do you realise that it is now illegal for this to be done on a DIY basis, it should be done by a registered Electrician (part p) you should contact a local sparky to give you a quote, I would say it would need a 10mm armoured cable, buried and labeled with safety tape,the cable may sound large but it is quite a distance, you have to allow for voltage drop over that distance, by saying 10mm that is an educated guess as I don't have a regs book with me ,to do it accurately, but I would say from past jobs that will be ok, but please get advice from somebody local, penalties are quite high if people are caught doing work without being registered, Ray