You need to get a copy of your credit file from Experian, Equifax, and Callcredit - the UK's 3 Credit Reference Agencies and MCL Software who run Hunter, a mortgage fraud prevention service.(posted 7924 days ago)If your Building Society is one of the many mortgage lenders who supply monthly profiles of accounts to the agencies, your partner's account will be shown against his current address. As you could be shown as financially connected to him (anything in joint names can be used by the Agencies to prove this), the debt would appear on your credit file too.
To get it removed if it is there you need to obtain a Disassociation. The Information Comissionmer publishes a booklet called 'No Credit' which tells you what to do. Citizens Advice Bureauxs have copies.