Everyone has to do a CBT (compulsory basic training). But this will only allow you to ride up to a 125 for 2 years.
All the info you need is on the dvla website, my general advice would be to get the most training that you can so you can ride any bike, its a false economy to not do you direct access course (to ride any bike) as what you save in training you pay for in insurance.
At the end of the day riding a motorcycle is the best thing in the world and I wish you luck, also make sure you do some off roading its the best way to learn to control a motorcycle, good luck....