If you want to ride a moped or motorcycle you must first hold a provisional licence and take a compulsory basic training (CBT) course. This will enable you to ride up to a 125cc motorcycle or moped with L plates on. At 16 the maximum sized engine that can be ridden on a CBT is 50cc, once you are 17 this is extended to allow 125cc machines. The CBT certificate lasts for two years at which point if you have not taken and passed your full motorcycle test you will need to retake your CBT to continue riding with L plates.
Apex Motorcycle Training can offer the full CBT course for £90. This includes any extra training needed to get you through your CBT. The local training centre is located in Peterborough and full contact information can be found on their website: http://www.apexmotorcycletraining.org.uk.