Volvo have diagnosed the problem:
"We have diagnosed the problem with your car, The clutch on the super charger has failed (which explains both the burning smell and lack of power etc.
This is part is not available until next Wednesday as it has to come from Sweden"
I found this interesting article about twin-charging which shows the offending item. Of course the million dollar question is what caused it to fail?
https://www.roadandtrack.com/car-cul...-power-couple/
Cheers.