Just an update for you guys...
I went to my local dealer today and we scanned the P1018 CEL. The Lotus Description is "Valve not able to reach commanded position".
We attempted recalibrating the valve using the Lotus diagnostic tool, but the same fault code still occurs in Sport mode shortly after heavy acceleration, which leads us to beieve that the mechanical range of movement on the valve they're using is different to the factory exhaust.
Rotating the spring stops the error from occuring, but also restricts the range of movement on the valve such that it does not close properly, which in my case causes the valve to rattle between 1200-2000RPM (although nobody else I've spoken to has had the rattling issue).
Interestingly, the senior tech also explained to me that there is a pressure sensor of sorts inside the valve actuator, which detects the amount of exhaust pressure on the valve and adjusts its position accordingly, so it's not a simple Valve Open/Valve Closed arrangement.
Hoping they can do further internal testing to sort the issues out moving forward.