Currently you can sign up to get free credit reports from the leading three credit reference agencies for 30 days:
Equifax - http://www.equifax.co.uk/Products/credit/credit-report.html
Experian - http://www.experian.co.uk/
Callcredit - http://www.callcreditcheck.com/
It is extremely useful to check what all these bank accounts and credit card companies are doing to your credit file - especially if you are planning on applying for a mortgage or loan.
The downside to these deals are that you have to give them your credit card details. I have taken up these offers in the past and as long as you email the companies telling them you want to cancel your membership you will not get charged anything.
Quidco will give you £5 each for signing up to the free 30 day trials at Experian and Equifax.