Quote:
"a permanent fistula (for example, caecostomy, colostomy, laryngostomy or ileostomy) which needs continuous surgical dressing or an appliance
a form of hypoadrenalism (for example, Addison’s Disease) for which specific substitution therapy is essential
diabetes insipidus and other forms of hypopituitarism
diabetes mellitus, except where treatment is by diet alone
hypoparathyroidism
myasthenia gravis
myxoedema (that is, hypothyroidism which needs thyroid hormone replacement)
epilepsy which needs continuous anticonvulsive therapy
a continuing physical disability which means you cannot go out without the help of another person
cancer and are undergoing treatment for either:
cancer
the effects of cancer
the effects of cancer treatment
These are the only conditions that entitle you to a medical exemption certificate. If you’re not sure about the name of your condition, speak to your doctor."
Source:
https://www.nhsbsa.nhs.uk/check-if-you-have-nhs-exemption/medical-exemption-certificates