As the amount owed is less than �5000, you can use the Small Claims Court procedure.
There's plenty of information available on loads of websites but one of the best is the BBC site:
http://www.bbc.co.uk/crime/law/smallclaimscourt.shtml
If there's enough information on that web page for you to feel confident about going ahead, then you should visit your local County Court where you can pick up the relevant paperwork. If, however, you feel that you need further advice, then pay a visit to your local Citizens' Advice Bureau.
Hoping this helps,
Chris