Three-wheeled vehicles have some particular licencing requirements. If the front wheels are more than 460mm apart it is legally classified as a tricycle and can be ridden on a ‘B’ car licence by anyone over the age of 21. If you’re under 21 you’ll need to pass an A2 motorcycle test or buy the 125cc version of the Tricity, which just needs a CBT (compulsory basic training) certificate.
Some insurance companies still require a CBT, please check.