I did something similar to @cgg in July, with my OH who is also new-ish to cycling!
Wednesday 7pm train Waterloo to Portsmouth and the overnight ferry to Le Havre, which was fantastic.
Thursday to Sunday cycle Le Havre to Cherbourg, 80ish kms per day (first bit out of Le Havre is very crap, lots of big roads and lorries, but after that it's pretty sweet and quite varied).
Fast ferry home Le Havre to Portsmouth on Sunday afternoon and train back to Waterloo, home by 10pm.
Yeah, get in/out of Le Havre is horrible if you want to cross over the Normandie bridge (which is a challenge in itself...) I guess it can be made much nicer if you cross with the ferry at Quillebeuf-sur-Seine, but that's quite a detour.
I did something similar to @cgg in July, with my OH who is also new-ish to cycling!