Hi Joe,
As Mike said its about your diabetes control, general health and hypo awareness/frequency, I haven't had to have a formal medical, just the chase around to see specialist opticians etc to please DVLA!
I would be tempted to make an appointment with your diabetologist to discuss if they think you'd be suitable to pass the medical, DVLA can be funny about releasing such detail. Your GP is perhaps less likely to be as aware about what DVLA are looking for and your suitability.
What we need to keep in mind is if you're newly diagnosed and your license has just been restricted DVLA may well consider there isn't enough history about your control to be able to grant an expansion to your license at the moment. And may perhaps want to consider your application again at a later stage.
On the point of employment, as a diabetic you're covered by the DDA (Disability Discrimination Act) as such your employer might not be able to just heave you from their employment. Its not like drink driving where you can loose your job as you're unable to meet the requirements for your position.
The DDA requires that the employer makes 'reasonable adjustments' to cater for the disability. As such they may offer you a smaller vehicle to drive or an alternative job either on a permanent basis or until DVLA say yes. Of course driving is also subject to their insurers being happy to extend cover to you.
Good luck, hope you're back on the road soon!