I think it's all wrong that you think you should able to walk into a doctor's surgery and expect them to just sign a medical declaration without doing some simple checks and making a small charge for it. BP and urine test are a minimum I would expect; relatively easy to do but should give some indication of your general state of health.
After all if you go to an optician, dentist. solicitor or any other professional service you would expect to pay. Or perhaps you expect the NHS to pay for your flying too on mental grounds!