Thanks for the responses.
I did go and buy one, number 9125. It appears to have been well looked after by the previous owner. It has the standard Mermaid engine and the Stern Powr leg. It also had new Ribcraft made tubes a couple of years ago.
It has a steering leak which I've temporarily 'fixed' by cable tying a cloth around the steering column. I've bought a new seal from ASAP Supplies near Lowestoft but having done a similar type of seal on my motorbike I'll wait until I'm not impatient to use the boat before attempting the repair.
I'll use the winter lay up to get more acquainted with it and do some tinkering. I can see a bigger fuel tank being added. Vetus do a 170 litre tank which looks like it would fit between the longitudinals. Does anyone re-circ their fuel through a filter to polish it before it goes, via another filter, to the engine?
Stern Powr - I've noted the comments on availability of parts. I found a firm called Midland Marine Propulsion who advertise Stern Powr stuff although I've yet to try them.
I just need to learn how to drive the thing now.