Actually, IIRC insulin is classified as a Pharmacy-Only medicine in the UK, rather than Prescription-Only, meaning that it can be sold by a pharmacist without requiring a prescription, to address
exactly this sort of situation.
Even if they've reclassified it as a POM in the 25 years since I stopped doing that stuff for a living, if you could have found a pharmacy in the UK, then under the Emergency Sale and Supply regs the pharmacist could, on their own recognizance, dispense a sufficient supply of prescription-only meds to get the patient back home.
(Caveat: I am an ex-pharmacist. Any advice I could conceivably give you is over two decades past its sell-by date and needs checking.)
Edit Current emergency sale and supply regs are described here:
http://www.nhs.uk/chq/Pages/1011.aspx?CategoryID=73&SubC...