We did that route last time (we’re cycling London to Paris again this year but via Newhaven and Dieppe as we loved it so much).
We chose the coastal route from Calais to Amiens on the EuroVelo 4 then went inland from around Noyelles-sur-Mer through Abbeville to Amiens. We chose it because it was a flatter route than the more direct inland one and because we liked the idea of cycling near the coast on the EuroVelo route.
It was well sign-posted before we came off and went inland and its certainly very beautiful in parts but it added around 40 km to an already long day and there was a bit of a cross-wind which made for a pretty exhausting ride which we really felt the next day. We clocked around a wapping 130 miles that day!
I’d say for cycling from London to Paris it’s best to go inland. Don’t get me wrong it was a great route but it added too many extra hours of cycling. I’ve not cycled the inland route so can’t say what that’s like but I hope that helped James.
