Hi there
No, I'm afraid 24 hour pumps will n ot take UK credit or debit cards, only French Cartes Bleus. Motorway service area pumps will be manned all night however, so suggest you stop at the first one you come to as they can take cash or UK credit/debit cards. Although fuel is more expensive here, the diesel is still cheaper than in the UK at the moment. About 30 euros worth should get you here. At Le Mans fill up at any Supermarket during opening hours - they will have a booth open (usually until around 19.00 in rural areas, 20.00 in big towns). Pay cash which you've got out of an ATM (these do take your cards).