The UK’s new Drone and Model Aircraft Registration and Education Scheme can be found at https://register-drones.caa.co.uk/
There are two elements to the online system.
Anyone responsible for a drone or unmanned aircraft (including model aircraft) weighing between 250g and 20kg will need to register as an operator. The cost for this is £9.00 which is renewable annually.
Anyone flying a drone or unmanned aircraft (including model aircraft) weighing between 250g and 20kg will need to take and pass an online education package. This is free and renewable every three years.
Both of these requirements became law on 30th November 2019.
You can find more information on arrangements for approved operators and model flyers plus new exemptions at https://www.caa.co.uk/Consumers/Unmanned-aircraft/Our-role/Drone-and-model-aircraft-registration/
Labelling your drone or model aircraft
You must label every drone or model aircraft you’re responsible for with your Operator ID. Use the same Operator ID for all your drones or model aircraft.
You can find your Operator in your confirmation email or online.
Drone labelling details (PDF)