As A7 UFO has said it could be a number of things
Limp mode =
Faulty N75
Boost leak
Sticking turbo vanes
I've also experienced when a pipe from the exhaust manifold to the EGR broke off and vented gases
Have a poke around your engine bay and the sides of the intercooler at the front to see if you can see anything obvious like a loose / disconnected pipe
There are a couple of people in and around your area i believe who have VAG COM - might be worth getting in contact with them to see if they will help you out for a few beer tokens
