Medical exemption certificate for Essential Thrombocythaemia

I have had ET since I was 33 and was very ill for 5 years with fainting, tiredness, constant anaemia but now 19 years later my symptoms seem to a lot better now and I only have to take aspirin, my platelets still run at about 550-650 though. I have always had a medical exemption certificate that my original haematologist told me to apply for but my new consultant says I’m not entitled to one because this is not a cancer!! Has anyone else had this problem? And is he right? And to all ET sufferers who are newly diagnosed please stay strong I was very young to get it but the symptoms has lessened now I’m older xxx