There are three main Credit Reference Agencies in the UK (Equifax, Experian and TransUnion) all of which calculate different scores.
If you are accessing your Credit Report via TotallyMoney or Noddle(CreditKarma), the Credit Score you are shown will be calculated by TransUnion. If you are accessing your Credit Report via Clearscore, the Credit Score you will be shown is calculated by Equifax. Experian also provide their own Credit Report and Credit Score services.
Your Credit Score will differ between the three Credit Reference Agencies, as they all use different calculations to determine your score. Lenders are also not required to provide information to all three Credit Reference Agencies and so you may find that some information is only held by one Credit Reference Agency rather than all three. Therefore, your Credit Score may be different depending on the information held.
When applying for a credit product, lenders will calculate their own score based off the information provided by the Credit Reference Agency. It is therefore helpful to check your Credit Report with all three Credit Reference Agencies before applying for credit.