So, what about free.quickcreditscore.co.uk, powered by Adaptive Affinity Limited? You are invited to "join now and get direct access to your free credit report and score". Their information (credit report and credit information services) is provided by Callcredit Ltd, and is free for the duration of your 10-day trial membership. There are two pages of information to fill out, including a checkbox to untick labelled "Send me special offers from Quick Credit Score and partners." You may get random errors on page 1: they may expect a zipcode (max length 5 characters) in the post-code field, and there's a random email address error: "Invalid characters in city". Just submit the same info again and you should be ok. For page 2 you need to provide telephone and credit card details, and you get the comforting message:
After successfully submitting your form, you can start taking advantages of your 10-day trial membership FREE of charge.
You can check your CallCredit credit report as often as you like without negatively affecting your credit score.
If you cancel your membership before the ten days are up (by emailing, calling or in writing) then no fees are payable. However, if you don't cancel, then you start paying a monthly membership charge of £29.95 - and continue to pay this until you say otherwise.
Bear in mind that Experian charges under £10 per month for what I reckon to be the same service, only there isn't a free trial with them. If you can possibly remember to cancel your quickcreditscore trial membership then it's worth it; otherwise, don't even bother.