Well, had the entire exhaust off today. Lots of water in it so I emptied it, dried it out with heat gun and refitted. Guess what.. Still smoking!

Also fitted new air and coolant sensors as I had them. Put another 20 litres of super unleaded in as fuel was getting low. Wonder if the fuel tank could be covered in condensation inside? Took car for a spin up the private track, let it idle for a bit, 2k for a minute then 3k for a minute. Still have the same symptoms. No smoke when first started (cold or warm engine) then white smoke/steam after a few minutes. I noted the smoke is only really at idle, if revs are held above 1500rpm the smoke stops.

Took new plugs out again and they are black like the last set after 2 days, mainly carbon with light oil on a couple.

Still no coolant loss and oil still clean. No mayo on oil cap but I did notice mayo starting in the flame trap when checking breather pipes still clean again.

Cancelled the mot today due to this issue but I've rebooked for tomorrow morning. 5 mile drive there which may help a little. We will see what happens!