OK, so the problem was a dodgey earth cable in the engine bay that rubbed against the block when accelerating, eventually rubbed through, shorted out, caused a fire in the fuse box and melted the entire wiring loom
Optimistic as always, I'm having it all repaired as I've done so much to the old girl already, it would be daft not to, besides, I like her and when she's running, she's a booty!