You must be aged 16 or over (or 14 or over in Scotland and Wales) to register to vote in the UK.
You must also fall under one of the following categories:
You’ll be asked for your National Insurance number (but you can still register if you do not have one). After you’ve registered, your name and address will appear on the electoral register.
You’ll need to print, fill out and send the form to your local Electoral Registration Office.
You can use the online service to register to vote if both of the following apply to you:
Passport details may be required.
You can get help registering from your local Electoral Registration Office.
The UK government also has an easy read guide about registering to vote.