Well, Oliver's called back.
Regulator rectifier broke down & overcharged the battery, killing the battery as well.
They say because it's hard to get to, the labour will be big too.
I'm a (mature age) uni student, so really don't want to fork out a grand$$ on repairs, so its going into the shed until July holidays, where I'll get to spend some time learning alllll about the rear end & electricals of my bike.
In the mean time I guess I'm off to ebay for parts.
Needs a service anyway, so I can do that at the same time.
Thanks NTRebel & Phil.S, in a way it WAS the dead battery that stopped me, but the cause of the dead battery is the big problem!