After weeks of annoying spluttering on full boost in 5th gear, I have found the problem, both hoses from the actuator had small holes. A quick snip and new cable ties means the problem is now sorted! All i done is trim off the old split hose and join the new hose.
What a difference, my boost gauge now shows full boost at 20 psi instead of 25/6 psi.
Bear in mind it is a TD05 turbo, so it has been mapped to run at 20 psi.
The car is off to Subaru for diagnostics for ABS light & maybe a new cambelt.

So all of you with fuel cut, check the hoses carefully, it does pay off to really look!