Hi --- Health insurance is covered under the General Insurance Standards Council's rules; this applies as long as the person selling or advising on the insurance is a member of the GISC, so you should check. All insurers must treat your details, especially medical details, with absolute confidentiality.
By law, all insurers or advisers who are members of the GISC must have a complaints procedure in place. If you have a problem or complaint about your coverage, talk to your insurer or adviser. If there's no solution, there must de an independent dispute-resolution procedure, and you must be given details of this when you take out coverage.
If you do not get a favourable decision then lodge a complaint, it may still lead to a delay for which possible compensation is awarded to you.
http://www.c-i-p.co.uk/gisc.htm
PS -- To add the GISC is a voluntary body members have to abide by the rules of if they are members, if you find yours is not a member then the FSA are the main regulator of insurance based products, you can take a complaint to them.
http://www.fsa.gov.uk/