From Koblenz stick with the Rhine to Hook of H , or switch to moselle  and the NE French coast, and get to the Hook that way before crossing over. Hook is needed as it makes getting home to Norfolk much easier

your views on the more attractive of these options please

Great to read of your plans Roger.

I think much depends on how much time you have and what your interests/priorities are. There's some attractive and interesting stuff, at least to me, either way. 
The Moselle to Perl is delightful if you like looking at pretty villages, hills and vineyards, more varied after that. One option to consider perhaps is to continue to Toul, then the Canal de la Marne au Rhin about 20km to Pagny sur Meuse and continue north on the EV19 Meuse route. Some country roads and cycle paths almost to Sedan, after which it's mainly cycle paths to HvH. Varied scenery, through the Ardennes, a more industrial day in Belgium then delightful rural Netherlands to Rotterdam. For me, at least, much more pleasant cycling than cross country to the French coast. Good luck with your trip.

Time is  unlimited..........delighted to have this idea, so will now devote time to having a careful look at this suugestion .. HvH is important for getting back to Norwich .. but how best to do it after theRhine/ Moselle junction is relevant .. not too hilly , not too much industrial area .. is what i am looking for.. so many thanks for your help

roger

studied route carefully . .. it puts   sbout 500kms extra on .. and the lumpy bit near luxembourg would be very tough for me these days....thinking about doing some of the bit to Perl and then returning to Koblenz  adding maybe 200 or so kms and then onto HvH.

Hi again Roger.

In case it helps I've attached screenshots from the Cycle travel app showing  the Meuse river route, which runs west of Luxembourg, and elevation profile. First is Pagny s/Meuse to Mouzon. The 100+m ascent before St Mihiel is easily bypassed just to the west, crossing a much lower part of the spur.

Below is the route and profile from Mouzon, from where there's a great cycle path (Route Verte, I think) all the way to Givet, then through to Liege near the Netherlands border. 

It's certainly longer, as the Moselle heads south westish from Koblenz, but it's a very pleasant route with relatively few ascents and much of it on good cycle paths. Enjoy your trip.