Ok, so I managed to get some logs this morning.
Injectors reading perfect.
The first log shows 3rd and 4th gear pulls and going into limp.
The second log shows various pulls but not going into limp.
MAP readings seem high to me, indicating 23psi just before limp, and 22psi on the other pulls, so it looks like 23psi is the trigger for limp mode. I understand boost shouldn't really be over 17psi or so, so its definitely over boosting. (Its definitely a standard car, its not remapped).
Also, on the cold / limp log it seems like the MAP flatlines before going into limp at approx 3000rpm. You can clearly see the drop in rail pressure before it goes into limp which I'm sure is the ECU trying to pull it back before shutting it down.
On the hot / non-limp run there is a consistent spike in VNT request and MAP at about 2800rpm which then tails off, so I think when warm it can just about pull the boost back enough to prevent it from going into limp.
Fuel rail pressure seems to be as expected, as do MAP readings.
So I'm thinking that its a VNT issue, but I need to test the Turbo Control Solenoid (VNT Regulator). Does anyone have any other ideas? It looks to me like the turbo is going to have to come off for a strip and clean, eugh.