Just to be pedantic - Those services in the first link are optional. You can use them, but you don't have to use them.
You can access your (what used to be called the statutory) credit report without using them. The 3 agencies all allow it online now, with only one or two hoops.
@hippy
MSE is a good place to get the info: https://www.moneysavingexpert.com/loans/check-free-credit-report/
And there's a whole thread on the forum about how to use GDPR to get the info they hold on you: https://forums.moneysavingexpert.com/discussion/5844570/credit-file-and-gdpr