In reply to adventure_vulture:
Lloyd,
A couple of years ago, three of us drove to Portsmouth with the bikes then left the car cheaply at a place found on Justpark.
Took the ferry to Santander then cycled up the Spanish and French coasts to La Rochelle and from there made a beeline for Caen and ferry back to Portsmouth.
We took 3 weeks but we camped every night, so carried extra gear - plus our average age was 70 and none of us are 'full-time' cyclists.
So 2 weeks would be very feasible.
When I was researching the trip, I saw that loads of people follow the coast up through Brittany to Roscoff but you then have to get back from Plymouth to Portsmouth (unless you use trains instead of the car).
An alternative to shorten it is to go to Bilbao instead of Santander.
Dave