Just to update this thread with good news that hopefully may help others with the same P1031 fault code on their FSI.
After doing the suck test recommended above, i went ahead and purchased a new Pierburg solenoid valve (which my VAG hand held code reader had diagnosed as the fault) and fitted it this afternoon.
I am delighted to say that the fault code is no more and having giving the car a thorough work out cannot get it reappear.
Previously the fault code would instantly appear after being deleted and occasionally the engine management light would accompany it too.
So I'm delighted to declare it officially fixed!
Just to note, the Pierburg valve (which is the same as the original one fit to the car from new 20 years ago) goes under a variety of names from egr solenoid valve, to manifold change-over valve, to bypass regulator valve, inlet manifold runner valve and so on and there are also many different variations of part numbers.
There are also lots of other manufacturers making similar parts, many cheaper but I was adamant I wanted to only use the original Pierburg one to avoid any potential problems.
For reference the OE part number is 037 906 283 D but the correct Pierburg one for the FSI will not wear that part number anymore and is now 7.28098.04.0
Strangely enough the usual parts suppliers Euro Car Parts and GSF don't carry them and can't get hold of them but they are available on Autodoc although i have never personally used them.
Anyway I'm delighted to be report my good news and to have saved a nice FSI from potentially becoming tin cans and i hope this also helps someone else in the future too