Hello Daleyo
I am a HR manager with Type 1 Diabetes. Basically from an Employment Law perspective you are not legally binded to disclose any Medical related conditions. Therefore you are not obliged to disclose that you are a Diabetic with either the Agency or the Company you are working for. In the same way, the Agency cannot penalise or force you to disclose a medical condition. When disclosing a potential protected characteristic such as a medical condition, the Employer can request for you to attend an Occupational Health appointment. This is not a bad thing, in fact in my Employment OH reports provide advice to Employers to support you in work with your medical condition. OH advisors will also inform the Employer whether you have an underlying medical condition which is likely or unlikely to be considered a disability with accordance with the Equality Act 2010. The Disability definition under the Equality Act 2010 is different from a medical Definition, and it is for an Employment Tribunal to determine this (which is why they say likely or unlikely in an OH report). If it is advised that your Diabetes is a likely to be considered a disability in accordance with the Employment Law your Employer is legally obliged to consider reasonable adjustments. Such adjustments could be more frequent breaks to manage hypos or to allow you time to test your blood glucose or it may be a room or a First Aid room to administer insulin. These adjustments may be recommended by OH however is not an automatic right, your employer will need to determine whether the adjustments can be supported within their business and depending on the type of work you undertake.
Therefore, it is up to you if you wish to disclose the medical information. However if you do not, and you have a hypo they may not know what to do. Additionally, by disclosing that you are a Diabetic, they may be able to put things in place just in case you need them to support you in work and manage your Diabetes.
P.S - My advice applies to what I understand from the Employment Law and Type 1 Diabetes and my employers are not involved. I also have to disclose that I am not legally trained and this is simply guidance based on my own knowledge. Culture, Operational needs and Business requirements may be different in other workplaces, therefore each case should be based on a case by case basis.
Hope this helps xxx