In reply to Matt Vigg:
This may or may not be of help:
http://www.ukclimbing.com/forums/t.php?t=523273
As a matter of interest, were you driving a UK registered car at the time or a French registered one?
My understanding is that they can send the fine but at present you don't have to pay it. However new reciprocal laws across Europe in 2013 will allow for prosecution and the ability to collect if you don't pay.
By the way, if you don't pay it, don't expect to drive the same car in France in the future without being pulled up by the gendarmerie! (My reason for asking about the car.) I recently read that a motorcyclist who'd fairly recently received a French speeding ticket through the post (and had decided to ignore it) was immediately picked up by numberplate recognition cameras at the ferry port on re-entering France on the same bike, was stopped and arrested and then escorted to an ATM to pay a 500 euro fine, a sum much in excess of the original fine.
Again, at the moment they cannot enforce points on your licence, but from 2013 any EU country can enforce them via the DVLA on your UK licence.
Not so good news perhaps ....
Dave