UPDATE
You lot are awesome. Thanks again for the great info.
So, this week the car went into TuningWerkes, and Reuben and his team worked through the problems i described above. The service these guys provide is top notch, the level of knowledge Reuben and his team have is seriously impressive!
Results: She is now back to her normal self! MPG is back on par and we even dropped in the APR re-flash (although drove it on standard mapping for a good while to test it out)
What changed:
1. Plugs had seen better days, swapped out with NGK Iridium
2. PCV replaced
3. And as you all thought, Cam belt was 1 knotch out!!
Before:
After:
So, i'm going to have a bit of a moan at the original dealer to see if they can re-fund some of the initial cost... i'll let you know how that goes!
Thanks guys, and huge credit to TuningWerkes who i'll definitely be going back to in future.