Sometimes your credit worthiness can be harmed by the actions of other people. One such scenario which is currently grabbing the headlines is that of identity fraud, but a more common reason is that your financial history has become linked to someone else's.
The most common reason for this is marriage or living as a couple, where a joint mortgage and/or bank account is held in both names. This will link the credit files of both people involved, and even following divorce or seperation entries on one credit file affect the other.
Another possibility is sharing an address - or even just a postcode - with someone of the same surname, either at the same time or within a period of a few years. Sometimes this can create the appearance of a financial link between two people even if this isn't actually the case.
In both of the above situations, if you find that the actions of someone unconnected to you financially is having an effect on your credit rating, you can file what is known as a Notice of Disassociation.
This is simply a letter you send to the credit reference agencies stating that there is no shared financial connection, and if necessary providing evidence that any previous connections have been dissolved. Examples can include a letter from your mortgage company confirming that the mortgage has been moved from being held in joint names to being in your name only.
All being well, the two credit files will be seperated and your credit rating will no longer be influenced by the other person's actions.