You can apply for a medical exemption certificate if you have one of the following medical conditions:
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
I had to copy in order to get my head round who can apply for exemption:
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.