Most insurance companies are a member of the General Insurance Standards Council (GISC). This is a new governing body that is in charge or regulating the insurance industry and setting insurance standards in the UK.
When making a complaint, your initial contact should be your insurance company, this should be done in the form of a letter. If for example you have not received the amount you expected in a claim, then write down all the reasons why you believe you have been underpaid and provide any evidence to back this up.
If you still don’t get anywhere and decide you want to take the issue further you should find out what the companies complaints procedure and follow this. This will either be in the form of an ombudsman scheme or an arbitration scheme. The difference is that you and the insurer have to commit to the decision of an arbitrator, however only the insurer has to accept the decision made by the ombudsman. If you don’t think the ombudsman decision is right, you have the option to go to court.