Space saving spare tyres

Looking for a new tow car and finding that many only provide space saving spare tyres.  I thought that it was illegal to tow while using a space saving spare, is this the case?  Some vehicles I've looked at recently have full size diameter but "skinny" tyres, are they legal or not?   Car dealers could not answer these questions, does anyone know for sure?   I tour a lot in France and other european countries and would need to be both safe and legal if i need to use my spare wheel.