No the UK don't have anything with a flooding well (other than the large amphibious ships Fearless, Intrepid, then Albion and Bulwark, with the RFA having the Bay class of ships too). But these all flood for larger boats such as landing craft, etc. All RIBs in the RN are launched from cradles/davits/cranes (unless as part of a larger flotilla going from the back of one of the above ships).
I think the Dutch or one of the Scandinavian navies may have these though.
There's weather out there - must be time to RIB!
(Or dive, or ref rugby, or.......)