In case anyone is interested and suffering similar issues, the problem stemmed from a knackered intake manifold runner control (IMRC) motor which operates the runner flaps. The IMRC unit operates by sending current to a motor which rotates a pivot attached to an arm - this arm attaches to the runner flap spindle in the intake manifold and adjusts the angle of the flaps as a function of, as far as I can tell, revs and/or engine load. The unit itself is only driven in one direction by the motor and relies on spring tension to return it to its original position. A spring is used so that the flaps open instantaneously when you bury the throttle to maximise airflow into the chambers.
However, as in my case, the main shaft bearing in the motor can fail and seize over time, adding friction to the system and adding delay to the flaps opening. This can cause some weird drivability issues and give you a flat spot in acceleration as I experienced. People all over tinterwebs will tell you that you have to buy a whole new unit at a cost of well over £100, when in actual fact the only component in the IMRC that failed was the motor. I cracked the unit open and it was in great condition bar a buggered motor.
Tracking down the motor wasn't easy as the company that manufactures them only operates B to B...but you can buy them individually from aliexpress for the eye-watering sum of...~£10:
https://www.aliexpress.com/item/32980964393.htmlNB: this particular motor will only work in early 2.0 TFSI engines i.e. AXX, BPY, BWA engine codes. It will fit the IMRC with part number 06F133482 - if your IMRC unit is printed with a part number with a letter at the end, you will probably have to find a different motor.
Happy to report that the new motor works flawlessly so far - its returned the throttle response and gives much better fuel economy when cruising. Removing the IMRC was far more of a pig than replacing the motor itself, if anyone'e interested I'll take some pictures and do a DIY.