I went back first thing today and moved the boat.
I couldn't stay on long as I've got a mooring buoy off freecycle. A nice big one that used to hold a 25 footer!
I got it home and I've already painted my mooring number on it. I just need some chain and a concrete block now to complete the mooring. No sign of chain on freecycle though.
I did try and wire in the charging circuit this morning, but I noticed that there wasn't battery voltage at the socket on the transom. Looking underneath the wires underneath the socket leading to the battery have been cut or corroded away, so that's something I'll have to replace.
Tracing the wires back through the boat ended up at this device:
Its marked P.R. Boat Specialities, Brooke, Rutland, LE15 8DE.
The output is 12V DC, but the input is AC, so I assume its some form of rectifier/regulator that smoothes the output of the engine charging coil to DC for the battery.
Anyway its another link in the charging chain that needs sorting before the engine can charge the battery. Not a biggie.