Here is a summary of the key rules for registering .co.uk or .uk domain names:

Who Can Register:
There is no residency restriction: Anyone in the world can register a .co.uk domain. You don't need a UK address or an EU address.

Technical Requirements:
Length: The total domain name (including .co.uk) can not be longer than 64 characters.
Characters: You can use letters (a-z), numbers (0-9), and hyphens (-) in your domain name. However, hyphens can not be the first or last character.

Accurate Contact Information: You will need to provide valid contact information during registration.