i'll stick my neck out & say it's closer to "driving under the influence.?"
No neck to stick out as it is already illegal in England, Scotland and Wales to drive with legal drugs in your body if it impairs your driving. However just having a one off Hypo would not be enough to prove the offence and realistically some form of recklessness or intent would be needed.
Also the practicalities of proving this in relation to too much Insulin would be very difficult indeed. As a roadside drug swab does not detect insulin the Police would have to carry out a US style Field Sobriety Test. If you fail that then it is off down the nick for a Blood/Urine test. Although by then you are probably already in the back of an Ambulance if the Hypo hasn't been treated.
I haven't been able to find one case in the UK although there have been cases in the US where certain breath test machines have shown positive for alcohol in Diabetics experiencing a HYPER due to increased Acetone levels in the breath.
The effects of a Hypo can be used as a defense in other crimes where "intent" has to proven such as Murder although Manslaughter is always there to ruin the perfect "get out of jail" excuse.