What cc motorcycle is a 16 year old legally permitted to drive in England?

A 16 year old is only permitted to ride a scooter of below 50cc in the UK- that is, above & including 49cc. They also have to wear a crash helmet at all times, and display 'L' plates on their bike. Sixteen year olds are also allowed to drive tractors on UK public roads. These are now the only motor vehicles that under-17s can drive legally in England (unless they are registered disabled, and have been given special dispensation to use an invalid-adapted vehicle).