Thanks for that Fiachra. There does not appear to be a facility on Autocom to check the boost pressure as you prescribe nor turbo control. I might have to check if my ACR4 can provide this information. I am reliably informed that all turbo pipes have been checked for leaks although one pipe is deemed as "soft" and may be collapsing under acceleration. This will be checked later today.
UPDATE: By removing the pipe from the MAF to the turbo, it is now established that the turbo spins freely but at this stage has not been inspected fully. Indeed, as previously mentioned a turbo whistle can be heard from the exhaust.
To establish if there is an exhaust blockage I might have to nip down to the garage armed with my vacuum gauge to see if there is a suitable take off pipe on the inlet manifold. Another thought perhaps is that although the MAF might be functioning correctly, perhaps there is a wiring fault allowing incorrect information being relayed to the ECU.
It is interesting that this vehicle was running OK until immediately after the service whereupon the problems manifested themselves. I also have now gathered that the original 5 - 30 oil is acceptable for this vehicle.
Regards
Pete M