Thanks mate. No, we'd like to be on the slopes tomorrow morning if poss! I've got a French "Carte Bancaire" which might have better chance in a 24h garage than an English one, but... I can't see them selling snow-chains from an unattended card machine like they do for fuel!!
We'll ask at the vehicle rental desk too, but I've found in the past chains are actually cheaper to buy than rent for a week!
Cheers for asking around, anyway...