Yeah, I started work for a UK Ambulance Service Trust 4 years ago (I won't say which one as i don't want to fall into the trap of posting anything about the trust online blah blah blah). At that time, they had a blanket ban on Insulin Dependent diabetics driving on blue Lights. The DDA doesn't come into it - the Ambulance service were just at the time following DVLA guidelines which roughly stated that "it is not recommended that anyone with diabetes drives on blue lights however it is up to each individual Trust to make a decision".
I challenged that 3 years ago with my Trust and in conjunction with my consultant, DVLA, Occu health and the Trust board, new New Standard Operating Procedures were introduced within my Trust allowing people to come into employment with the Ambulance Trust as an Insulin Dependent Diabetic - One for the Diabetic driver and one for Control Operations.
Broadly speaking (and i may be forgetting a few here from memory) they are:
Diabetic must identify themselves with control and their crewmate (if applicable) as an Insulin diabetic at the start of the shift.
Diabetic must regularly check blood sugars before and throughout their shift (2 hourly intervals or as close as manageable bearing in mind the scope of the job) (i.e. if driving or with a patient, it isn't always possible to do your checks bang on the hour - they should be done with common sense in mind ASAP)
Diabetic must carry fast acting sugar products
Diabetic must wear an SOS talisman or other Medic- alert system
If sugars drop below 5, Diabetic must eat something
If sugars drop below 4, diabetic must inform crewmate, control, and Team leader. Incident must be investigated my team leader who should visit on scene to make sure diabetic okay. Driver cannot resume driving until 45 minutes AFTER blood sugars have normalised.
Blood glucose meters can be requested and inspected at any time by the Trust to ensure adherence.
I heard rumours of staff that were already ID (insulin dependent) being allowed to continue driving on Blues before this SOP was introduced but have seen nothing in writing to corroborate this.
BinnyBoo is completely correct - it all boils down to good control, proof of it and sticking to your guns. Perserverence