Yes, Hymie is right. It's the Insurance Ombudsman that you can contact if you have a complaint. (now part of the Financial Ombudsman Service)
http://www.financial-ombudsman.org.uk. However, have you tried speaking to someone in authority at the insurance company? Ask for the Claims Manager - don't be fobbed off by some person in the call centre. Insist on speaking to someone who can actually do something about this for you.
Before the Ombudsman will get involved you will need to be able to show that you have tried to resolve the issue with the Insurers. Have you kept copies of all correspondence and kept details of phone contacts?