I've been living with this error code and subsequent regular spells of limp mode for 3 months now. Been in to Autolusso (long way from Norfolk I know!) and they think it's most likely the turbo vanes sticking, after changing the vnt solenoid twice. I commute to Sheffield each week and stop/start the car as much as 10 times in a journey, although lately I'm losing the will and driving further and further in limp mode - it's surprising how 'manageable' limp mode is on a GT, although my journey is mostly single carriageway, so I need the full power to get past the lorries safely. I do find that towards the end of the journey it tends to stay out of limp mode - I guess perhaps a hotter engine helps. Also, not sure if the colder weather makes it worse.
I'm now contemplating trying turbo technics for an exchange turbo - see what they quote - I'm on 117K miles, and want to run the car another couple of years, so cheaper than changing the car. I could try the oven cleaner trick, but I'm not sure I'm up to the job of removing the turbo, especially in this weather and needing the car back on the road in a hurry.
Whereabouts in Norfolk are you? Did you use alfashop in Norwich - just wondered as I've never been there? Good luck with yours, it's a shame, takes all the fun out of what had been a superb car.