Initially there were codes coming up for the EGR which was replaced along with the EGR cooler, the cam sensor and fuel filter were also replaced. Although the car is still juddering it is not registering any fault codes. The Terraclean was just a way of hopefully cleaning any potential carp from inside the engine after reading the post about fuel additives. Although it didn't sort the problem it is running a lot better now it's been done.
The cars going back to the dealers in two weeks for another scrutinising so hopefully they'll finally get to the bottom of it