This is from a text over the dutch lifeboat-development
......In 1979 the first prototype was launched. The Mountbatten of Burma had a length of 12 m., beam of 4.35 m., and a draught of 1,15 m. The boat weighed 7.1 tons and could take 85 rescued people aboard. Two 212 HP Sabre engines each driving a Z-propeller, gave a maximum speed of 26 knots. The Z-drives showed to be no success and were later replaced by three outboard engines........
There is a big RIB diving boat based at Portland called Protector. She used to be called Eastern Protector & belonged to a Fisheries protection agency in Northumberland.
Her hull looks quite similiar to Swanage Diver & she is of a similiar size. I know the boat was around in the early eighties with an "Island" type wheelhouse so it maybe the "lost" Medina.