Turns out my engine is goosed! Getting the usual quote of £6k for a new one.... gut wrenching.
Luckily I have managed to exchange for a wee Audi.
Sad to see the roc go, but a new engine after 20k miles is stuff of nightmares!
Apparently this is a common fault with the 1.4 TSi engine accross all car types from VW, Seat and Skoda. However, good luck getting VW to confirm this...