This is all down to the definition of 'severe' and daytime and night time hypo awareness. The DVLA define severe as "requiring the assistance of another person". Like the DVLA said, they won't make any allowance for a severe hypo happening in the night. They also state:
So they would see having a severe hypo in the night as you not having good enough hypo awareness which would wake you up before it became severe. Due to them not distinguishing between day and night hypos, this would conclude to them believing that your day time awareness is not good enough to allow you to drive, hence revoking your licence.
The only thing that will change this is for the DVLA to distinguish between day and night time hypo awareness and unfortunately I can't see them doing that anytime soon.
All quotes taken from here:
http://www.dft.gov.uk/dvla/medical/aag/D/Diabetes - Insulin treated.aspx
Petition signed and tweeted as well.
offtopic: Nice to see another Martyn with a Y on the forums
🙂