[ymc30]

Just a quick follow up for anybody interested...

After having half of the car taken apart I gave up. Next day put the whole thing together and the problem was gone.

The Start-stop system has some fuses in the "engine compartment cold zone" which is really - I mean really - hard to reach hence the reason the car was in pieces. This meant that the supply battery was also disconnected overnight alongside with the main one. I don't know whether this done the trick?!?

Also first I connected everything up except the TCM which wasn't even plugged in to the gearbox. Obviously engine did not start.
Next up I connected the TCM to the wiring loom but not to the gearbox. This resulted a bunch of DTCs related to gearbox pressure sensors, etc. Engine refused to start obviously.
Finally everything properly connected - engine started first time. Still has some TCM related DTCs but I'll figure them out later.