After a few weeks of back and forth with VW and getting nowhere I ordered wheels and tyres from wheelbasealloys on Monday after getting confirmation from them that they would fit the PP GTI, they arrived today as requested and I've just had them fitted to the car.
Wheels still turn and I haven't ripped the brake calipers off so I guess it all works fine, irrespective of what VW say! I will grant them that there is very little clearance between the brakes and the inside of the wheel though. I'd post a picture if I wasn't ashamed of the state of the car.
For anyone else who is looking for information, it is a performance pack GTI and the wheels/tyres were 205/50/17 ET45.
Strong recommendation for
www.wheelbasealloys.com from me.