Without a court order, or your consent, the police have only the right to access medical records in order to identify a person involved in a serious arrestable offence and for no other purpose - assuming you are alive.
Police are able to request medical records to prevent / detect crime or apprehend / prosecute an offender and where failure to release the records would serious harm that purpose. This right to resquest this info is covered in section 29 of the data protection act 1998.
In practice police will contact hospitals or doctors and make the request in writing, usually with what is known as a section 29 form. Where the data holder does not believe the info is needed for the stated pourposes or declines release the police can seek a court order.