Firstly you need to write to Experian and ask for a credit history for your address. It will cost you a nominal sum of �2 (
http://www.experian.co.uk/
for details)
Once you've found the "hanging debts" on your address, you then need to contact the creditors in turn, explaining that the person who owes this money no longer lives at your address. They are usually quite helpful in clearing your good name, and will write to the credit agency to explain this. The Experian site has all the info and advice you need.