OK, they have all just got back to me.
The car was and has always been the performance pack version. Dealer was confused as all other "options" are shown on the order as "options" whereas the GTI Performance actually shows as a different model of car.
Because he could not see the "Performance Pack" option he believed it was not on there. He has apologised for the confusion and offered a tank of petrol with the car in recompense.
Although I am relieved about that, I just want the car today and feel like throwing my toys out of the pram and stamping my feet until it arrives!