To ride any motorcycle you need a full or provisional licence you can apply for one here https://www.gov.uk/apply-first-provisional-driving...
If I pass my full test on a 125cc scooter can I ride any cc scooter?
The answer is no and all new test categories for both motorbikes and scooters are listed below : Further information can be found at https://www.gov.uk/ride-motorcycle-moped
Licence category : A1 - Small motorbikes up to 11kW ( and a power-to-weight ratio not more than 0.1kW per kg) and 125cc.
Requirements: Minimum age 17 years, CBT, theory test and practical tests. If you wish to ride a larger cc then see category A2.
Licence category: A2 - Medium motorbikes up to 25kW (and a power-to-weight ratio not more than 0.2kW per kg) bike must not be derived from vehicle more than twice its power.
Direct Access - Minimum age 19 years, CBT, theory test and practical tests.
Staged Access - 2 years experience and a further practical test.
Licence category: A - Motorbikes unlimited in size/power, with or without a sidecar and motortricycles with power output over 15kW.
Direct Access - Minimum age 24 years, CBT, theory test and practical tests. You can book your theory test here https://www.gov.uk/book-theory-test and practice your theory test here https://www.gov.uk/take-practice-theory-test
Staged Access - Age 21 years and over, must have held an A2 licence for a minimum of 2 years and then pass practical tests.
(Practical tests are the Module 1 and Module 2 refer to the training section)
For more information regarding test categories please go to the Government web site. www.gov.uk