UPDATE
Tonight I changed the DIS pack, plugs, and leads, for brand new components. All OE stuff unfortunately, VX prices would have been prohibitive. But nonetheless proven on other cars.
I then removed the plate mark suggested, and checked the fuel connections on top of the tank. They are definately quite corroded, BUT, secure and not leaking.
I tried to start her up after this - just wouldn't go. I ended up flattening the battery. Put a can of petrol in - still nothing, despite the fact there was pressure in the rail when the release valve was pressed, and a spark on all plugs.
Charged battery for a bit, and got 2 more cans of petrol. After a lot of cranking and coughing, she then fired up.
At this point, I had a
result!She fired into life, misfire totally gone, smooth as silk. Comparable to a 40k mile engine.. really quiet, and responsive to the throttle (when I'd let it warm up, obviously!) 8-)
I let her idle for a bit on the driveway.. exhaust sounded... wrong. Blocked. I cable tied a rubber glove to it, and it wouldn't inflate the glove!!!!!
After letting it idle, I had a look under the fuel tank. Couldn't see any drips etc.
Took her for a spin around the block, I had covered half a mile, when the guy behind flagged me down.
"Your car's pissing fuel everywhere mate!"

Had a look, sure enough, puddle underneith. Inspection area still all dry though. Though I could smell petrol if I put my nose to it.
There seems to be a fuel mist everywhere... I am thinking, possible pin hole somewhere???
Now the engine runs so well, I just wonder if in fact, the fuel thing is unrelated, and an unfortunate co-incidence... :-/