If you are on insulin, there are special requirements to drive a vehicel over 3.5 tonnes, to ensure you are aware of risks and recognise symtons or an approching hypo. Normally 6 mths after starting to inject insulin, then dr's assesment.
See driving section on Diabetes UK website.
Any insurer must be notifed you have diabetes, as must DVLA, if diet only, or tablets, no porbelm wiht any vehicle licence.