Mark,
I'm afraid that's going to depend entirely on the terms of your contract of employment. There's no reason for any diabetic not to drive at night to be honest. If you are prescribed blood sugar lowering medications such as insulin or gliclizide then the DVLA need to know about it and your licence would be restricted to a 3 year term, as mine is.
I'd check this out with your line manager if I were you.
All the best,
fergus