Casinos need to protect themselves and the players against fraud by rigorous KYC (Know Your Customer) procedures. They also perform AML (Anti-Money Laundering) checks if they spot suspicious banking patterns.
After 7th May 2019, all casinos operating in the UK need to verify the following details before giving players access to the games:
Name
Address
Date of birth
In addition, casinos may need to know your source of wealth and make sure that you're not using banking methods registered to anyone else.