The UK doesn't have a central credit score.

There are central "Credit Reference" companies that record your credit history. Your bank reports that information to them.

The banks can then get that information and use it to calculate their own credit score for you. Each bank probably uses a slightly different scoring system.

Generally the credit reference companies will report:

• What loans and credit cards you have
• how much you owe on each account
• For each account, each month, whether you paid on time, how late you paid, or if you didn't pay at all. For the last 2 years.
• If you have a joint account with someone then they will report their finances too. Since if they get into financial difficulty that will probably affect your ability to repay too.
• If you are taken to court for non-payment, or declare bankruptcy, that will be reported for many years (maybe 7 years? Never applied to me so I'm not sure the exact duration)

You can get a copy of your own credit report for a nominal fee. (£2, about $2).