Hi benson,
If you going to Nantes from Central England, you might want to enter the channel via SAM, get a service off Solent I think it is, and then over to Cherbourg (MP NDB). From there you can almost get a pretty direct routing to Nantes via Granville (NDB), Rennes (VOR), and to Nantes(VOR). It might be worth planning an entry via the entry/exit points. NW would probably be best for you. You can get Jep VFR Plates with RNAV and Geocords for each entry/exit points to help you find them.
What ever you decide, enjoy the trip.
fair winds
obk