Thanks, I had a quick read of my Haynes (which I don't use a great deal) last night and then realised exactly where to look!!
I'll give it a coat of looking at later on and let you know what I find/whether I've been able to resolve the problems.
Now have it disconnected and tuner removed (what a pig the block is to extract if you've never seen how it works - and it's upside down!); it's been wet/possibly partially submerged but the connector block/pins all look OK slight tarnishing/salts on a couple of pins, just need a bit of a 'wash and brush up' and all the wires thoroughly blown off/dried. The arial connection however is knackered - the lead/pin end is really heavily corroded and cannot be saved, the socket on the tuner is corroded/tarnished but might clean up.
If I can find a replacement arial lead terminal (any ideas?) it will probably work OK.