So I have managed to get to the bottom of the underboost issues. There was indeed an issue with the MAF as well so I have replaced that. The car felt better afterwards but massively underperforming. I have thought to check the Waste gate actuator and when moving it it felt moving freely. So I undertook the task to remove the turbo out entirely to check if any hidden issues and also to check if the turbo is ok. Well, after an insane amount of hours fighting rusty bolts, I have managed to get it out to find....that the turbo waste gate actuator it was off entirely so the wastegate was just flapping about doing noting. I have used an e clip to secure it in place as there was nothing there to hold it. Turbo and wastegate door is in good condition, the impeller and bearing is absolutely fine. The car now performs as it should, making really good boost.
However I now have an intermittent fault , "cam 1 actuator cylinder 1 intermittent" but by the looks of the harness wiring loom is understandable ( its busted and frail so will need changing.
Have a look at the pics for everyone that has the same issue.