After a short time driving an overtemperature warning message appears on the centre screen and the vehicle goes into limp mode.

Confirmed coolant level is correct.
As per customer interview, viewed a new thermostat (housing assembly) had been fitted - Mahle brand, unlikely the new unit will give the same fault.

Test drive while monitoring coolant temp. Within 2 minutes of normal driving the coolant temperature reached 120 degrees, well above the 108 degrees rating of the thermostat, the overheating warning appeared and in limp.