The car insurance market is so competitive at the moment that many people, on shopping around at renewal time, can secure more competitive rates and associated benefits from alternative insurance providers.
Periodically however, particularly if a person has changed their vehicle near to their renewal date, been involved in an accident affecting their no claims bonus or in dispute with their insurer due to some kind of non disclosure of a material fact which may have affected their insurance premium of cover, there may be premiums outstanding due to the previous insurer.
If this is the case, beware that your previous insurer can legitimately withhold any evidence of no claims bonus until such time as they consider the matter to have been resolved to their satisfaction.
If you find yourself in this situation, whilst it may go against your principles, you are probably better advised to settle their bill now, and if the dispute is later resolved in your favour, request repayment of any overpayment made.
You also have the option of approaching the Financial Ombudsman Service for them to carry out an independent review of the dispute if you and your former insurer cannot negotiate a satisfactory settlement of the dispute.