One on one off Caretaker for the leads. I have made that mistake before
The old and new leads are having the same problem as are the old and new plugs now. My brother is meant to be coming round with an OBD reader in the morning so may have something to go on then.
Taking one lead off at a time affects the tick over more for each cylinder so am assuming now that it is not ignition related and looking at other things but cant work out what as didn't touch anything else.
No apparent air leaks or loose connections. Stumped.