been doing a bit more reading into this and found this over on ukmkivs.net:
Intermittent Limp mode on the diesels is often a small hole in one of the pipes under the bonnet, a symptom of this is it slowly getting worse over time and you being able to give it beans all the way to the redline yet 10 mins later motorway cruising it goes into limp mode.
You need to get it on vag-com, if its a pressure deviation message or something similar it will almost defo be a split hose somewhere
Good luck
and this too:
You'll find this is a common issue with the 110 TDIs - happened around 80mph, right? In order of expense, it'll one one of a few things...
The vacuum hoses going to the N75 boost control valve will have cracked perished (especially the small top one)
The N75 valve itself has gone
The hose between the intercooler and turbo has cracked / perished
the EGR valve and inlet manifold is clogged (although you can do this yourself - vwvotex have a good guide on it)
The vane lever on the turbo needs lubricating
The turbo needs a refurb / replacement
I would clean out the EGR valve and inlet manifold anyway as they have a habit of becoming clogged - especially if you run a remap or tuning box but more so with a tuning box.
Hope that helps
