From the Wiki:
In the United Kingdom, the three credit reference agencies are Experian, Equifax and Callcredit, which works closely with its US partner, TransUnion.
Most banks and other credit-granting organisations subscribe to one or more of these organisations to ensure the quality of their lending. This includes companies who sell goods or services on credit such as credit card issuers, utility companies and store card issuers. Subscribing organisations are expected to provide relevant data to maintain the common data pool.
Credit reference agencies are bound by the Data Protection Act 1998, which requires that data relating to identifiable individuals must be accurate, relevant, held for a proper purpose and not out-of-date. Individuals have a legal right to access data held on them. The Act specifically gives consumers the right to request to a copy of their credit file by post for a fee of £2. [4] The UK credit reference agencies will also allow consumers to access their credit report on-line free, usually giving free access for a trial period, after which a monthly or quarterly fee may be charged for continued access. These 'Statutory Credit Report' services are sometimes provided through specially developed and branded services such as Credit Expert from Experian and through commercial promotional services such as Credit Report for Callcredit.
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So, google any of the three credit bureaus and subscribe to one of their credit watch services - usually free for a trial period.