first of all the ferry from Calais to Dieppe does not exist.
If you want scenery +rurality + swimming options, you're better off taking one that takes you to St-Malo, Cherbourg, Caen or Le Havre. they leave from Portsmouth or Poole, take your pick.
I would consider going to St-malo ( full niught on the Ferry and arrival at 8AM) and returning via Caen, going south all the way to Nantes. should be about 600km.
first of all the ferry from Calais to Dieppe does not exist.
If you want scenery +rurality + swimming options, you're better off taking one that takes you to St-Malo, Cherbourg, Caen or Le Havre. they leave from Portsmouth or Poole, take your pick.
It's all very flexible and easy