Thanks Ravima - checked out my policy booklet and there's no contact details in there other than the general phone number I've been using all along.
I've taken your advice and written a letter to the general manager of the brokers, and the motor underwriting manager of the insurers. Outlined what exactly what I need from them and told them I'll go to the Ombudsman if they don't furnish the document. I faxed those through today and also sent the originals in the post. Fingers crossed that'll get them moving!