You can ride the tricycle legally on private land with the landowner's permission without any restrictions. However if you would like to ride it on public roads you need it to be registered, insured and taxed (and you need to be licensed).
You can purchase the tricycle from us preregistered or you can buy it unregistered and register it yourself. We also have a page on insurance providers we have had good experiences with. Road tax is £26 per year
If you have a full UK driving license and are over 21 you don't need any other license to ride the tricycle. Otherwise, you must take a CBT course (short one-day training/test combined). If riding on a CBT license, you cannot carry a passenger and must use learner plates.