Thanks for checking your readings Lizard, it points to my BPS reading high for sure.
Some manufacturers include an ambient air pressure sensor within the ECU (my old Mazda had one) and this was so that if the driver took the car to high altitudes the ECU would adjust the fueling to suit. Maybe the Volvo sensor is also inside the ECU.
The new sensor is fitted, just waiting for him to test it, to be fair I told him to take his time and fit me in around his other jobs as I have the use of our Twingo anyway.
Looking forward to feeling the restored boost under acceleration