Flat battery - anyone with jump leads ?

If you can't find a mate with jump cables, go to your local Brico or Auto 5 and buy a "Booster Batterie", which is a portable rechargeable battery charger. You should be able to get one for less than €50.
here are the Black & Decker models.
http://www.blackanddecker.be/fr/automotive/productoverview/hierarchy/2036/
It costs you less than a call out, and you'll have the kit for the next time you get a flat battery.