If you are looking coming to the UK for the main purpose of receiving treatment for a medical condition is required, you may consider making an application as a visitor for private medical treatment. However the individual would not be able to receive treatments form the National Health Service (NHS).
Extension of stay under this category is permitted but in order for an individual to qualify for an extension of stay as a visitor for private medical care, it is mandatory that the applicant fulfills the following requirements:
An individual who intends to extend his/her stay in the UK, for the purpose of undergoing private medical treatment, he/she must make available a letter form a registered medical practitioner. The medical practitioner must hold an NHS consultant post, or must be a Registered Specialist of the General Medical Council (GMC).
Switching into the private medical treatment category is permitted under the immigration rules, unless in situations where the last permit of leave was done under the Approved Destination Status Agreement with China route.