Anywhere north of Hadrian's wall you can generally do this. Although technically the wild camping rules are to access without power... No sure if that means you can paddle the Rib ashore
. But in reality if you cruise to somewhere where no-one can see you and leave no sign when you are gone no-one will bat an eye lid.
Take a look at some of the Cruises. And the Gurnard's posts for what you can achieve if you are up for the challenge!
In Englandshire, the rules aren't so flexible, but also there are less obvious sheltered spots out of sight to camp. So you might be looking for a proper camp site.
Do you need a pontoon if you go from somewhere else? Or can you anchor // pick up a mooring... And get ashore somehow?