Do i need a c.b.t to drive a 50cc with L plates?I?

-Yes you must take the CBT

click on the link and you will see the law...

http://www.begin-motorcycling.co.uk/law.鈥?/a>"All learner motorcycle and moped riders must complete a compulsory basic training (CBT) course before riding on the road. Find out how to take the course, and the rules that apply once you have done it."
Yes, a CBT is required to ride a moped (50cc) unless you passed your full car test before February 2001, in which case a CBT is not required as you will already have a full moped licence ('P' on your driving licence).
You need to take a CBT to legaly drive any motorbike on L plates in the UK and you can only drive up to 125cc.
if you are on L plates then yes CBT required