Hey mate,
I know a lad who lives just off junction 3 of the M5, as worked for VW for the best part of 18 years who fixes any of my problems at a fraction of the cost of a main dealer. I can have a word with him and if he's happy i'll give you his number??
With regards to your problem, i can had something simular. It sound like a possible issue with an injector/s. Does t feel like it is slower in acceleration?
If socould be the coil pack..?
With mine, someone hadnt bothered changing a faulty injector and tried to 'pack it' into position....caused a major carbon build up resulting in simular symptoms to yours.