Update – spoke to Motability this morning and they will pay for the replacement canister, so I’ve called my BMW dealer and they are sorting out the authorisation so that I can collect it on Tuesday the day before we go on holiday.
Quite a relief, as a puncture when I have 3 or 4 suitcases, a wheelchair and my wife in the car will be stressful enough as it is, without the added problem of having no means to repair the tyre ?