Thanks all!
I'll give all the earthing points a good clean up, something I'd never done.. I didn't realise it'd have such a dramatic effect!
Now to get me down to Maplin and on the hunt for a Visa alternator!
Really appreciate the help & advice!
Matthew

I found a reon one on ebay a year or so ago. I'll dig out the details of that as well and post it and the pic once I find the camera...