Misfire!
(Mot my engine pic)
I pulled the plugs and one electrode was quite worn down. It even seemed slightly loose, which I've never seen before in a spark plug.
I cleaned & re-gapped them all, plus tidied the electrodes in the dist cap & rotor. I'll swap in the plugs from my parts car's parts car (good thing I kept the engine) if they look decent.
Parking the irksome wee beastie SOON. 3 days & counting!