The cancellation fee should always be a reasonable amount, i.e. around £40-50 maximum. If they try to charge more, raise a complaint with them and then escalate to the Financial Ombudsman. Identify the current insurer that your broker has insured you through, the contact that insurer directly if you can. If not, contact another broker and see if they use that underwriter. Request for a quote on the new postcode with the same insurer. If they provide a quote with the same underwriter, you can go back to the old broker and advise them they are incorrect as the current insurer will insure you. The policy does not need to be cancelled and only a small administration fee should be charged.