Litto-miss-loz
I qualified as a RGN long before I was diagnosed and have continued to work in various nursing jobs since, although wasn't allowed to rejoin Territorial Army - I'd resigned hoping to emigrate.
As long as you pass the occupational health requirements, there's no reason why you can't train as a nurse of any type - general, mental health, learning disabilities, children. There's no compulsion to specialise in diabetes, just because you have it. You will need to cope with shifts, irregualr meal breaks, physically and mentally demanding work, although reasonable adjustments for your condition / disability should be made. Showing that you've thought about such things shows that you are responsible and a problem solver, which can only be good.
For definitive advice about training and practicing in UK, the governing body is Nursing & Midwifery Council
http://www.nmc-uk.org/
Nursing Times is the main weekly journal for nurses:
http://www.nursingtimes.net/ forum is especially worth a look - click on Opinion and Debate
Royal College of Nursing is another good source of advice, although not everything is available to non-members - see
http://www.rcn.org.uk/