Strangely no replies on this but an update, for those interested.
Well I got her going and now starts fine again. I don't think anything was wrong as such, as it had been running fine, so I just cranked and tickled the throttle until it eventually caught and started.
But, as well as the plugs, I did change the dizzy cap and cleaned up the rotor arm with a needle file which looked tasty. So I'm sure this all helped. I have had a new rotor arm and have been meaning to change it for some time, but not able to get old one off as bolt is seized. A common problem I believe. I have read that cutting off the rotor arm, which is just plastic largely, and getting needle nose vice grips (aka mole wrench/ pliers ) on the exposed head of the bolt is the way to go ??
Another issue is that the dizzy cap lower bolt is particularly exposed to the elements and has sheared, leaving the threaded hole in the distributor blocked. It will need drilling out carefully and re-threading/ tapping but, due to location, that looks like it has to be a dizzy out job ??
Emissions was fun again this year btw, MOT tester says cat has to be really hot and is too far back, so a new one wouldn't necessarily help.
As usual, any thoughts/ feedback on any of this is always appreciated folks !