Quick update on this:
Parts arrived for a new linkage as well as the Reely part from Conrad. Long story short, fixing the swirl flap arm has cleared all of those fault codes and Service Required light, as well as solving the loss of turbo.
Thanks to Stuart Bowes for the suggestions, I ordered some rod ends, and strut parts for an RC car separately to make a new arm. Rod ends are M3, plus 20mm M3 studs and 20mm M3 internal threaded spacers:
Here it is assembled, next to the Reely part. The quality difference in the bearings was considerable so I went with the self built option:
Finally, here it is installed:
It took a little it of extra work compared to the YouTube video example I originally posted. Mainly due to the fact that the actuating arm on the motor didn't appear removable as that example was. So I took out the whole motor and very sensitively cut and drilled the metal ball. The plastic did crack a little but after an araldite fix, it seems to be pretty strong. I'll keep an eye on it though.
After replacing this and re-scanning with VIDA, the fault codes for the MAF, turbo and swirl flaps are all gone. Taken for a test drive (town speeds only) and no more loss of power - everything feels good all the way up at take off etc. Starting engine when cold is also much faster and initial cold idle much smoother.
I was initially getting a new code of the swirl flap motor jamming when doing the adaptation through VIDA but it appears to have full range of motion end to end. I adjusted the length of the arm and it seems to have solved it intermittently but will check again after a longer drive this weekend. The callipers said it was 80mm hole centres on the arm as per the original. It could also be the bolt head on the butterfly is fouling on the engine casing (it's pretty gunky in there) or worst case I've damaged the actual motor when modifying the arm. I'll dig further soon.
Now that's out of the way, I've just got the other error codes of faulty internal air quality sensor, faulty ignition key light (this one is ridiculous!) and faulty A/C. But I'm quite happy to leave those indefinitely.
Moved on to some cosmetic work - plastidipped the grill / wheels / emblems and used some Gtechniq C4 Trim Restorer on the faded plastic bumpers, wiper arms, mirrors etc. I was sceptical (£20 for 15ml...) but it's worked extremely well and was more than enough to do the whole car's worth of plastics:
