Your employer has to make "reasonable adjustment" for your condition. As an example, an employer may have a "trigger" for a talk from management after 8 sick days a year, in your case, after discussion, you both may agree to make this 10. That's just an example. I sort of disagree that any health problem can be related to diabetes. If I am off sick with flu or a twisted ankle, my boss won't accept that is diabetes related. As for taking longer to get over things, again, I'm not convinced . I agree if I cut my foot it will take longer to heal, I also agree that flu etc may impact my BG levels but I've never read that I would actually take longer to recover from an illness ? Anyway, yes, diabetes is classed as a Disability and you have a degree of protection under The Equality Act but ultimately, it doesn't guarantee protection from dismissal if time off or performance became unacceptable.