I've replaced the plugs and coil packs, and warm running is fine now.

 

It had been starting fine, but it's 3c here atm and I just cold started it and it keeps running really low ROMs and dying or nearly dying.

 

This doesn't feel like electronic misfire anymore, more like fuelling.

 

Vid where this happens and recovers, including exhaust note.

 

https://youtu.be/LSmkLqLsZ-Q

Dodgy injector/wiring?

Maybe, got a 200 mile journey now. Will pull the plugs again later and read.

I had a very similar issue on my 1.8 Octavia and managed to diagnose a bad PCV.

If you have any or a mixture of these issues it could be the same issue on yours.

• engine misfires at idle.
• Lean air-fuel mixture.
• Presence of engine oil in PCV valve or hose.
• Increased oil consumption.
• Hard engine start.
• Rough engine idle.
• Possibly black smoke.
• Oil fouled spark plugs.   

There's a decent chance your PCV is stuck open I'm not going to get into it too much and I can't say I know enough about it to help, just adding my 2 cents based on what helped for me.