UPDATE ON THIS.
Further to having the PRV fixed my supercharger completely failed, taking with it the thermostat, and expansion bottle.
Apparently it had no oil in the gear chamber so the teeth wore down to basically nothing, this stopped drive to the water pump with inevitably led to the coolant overheating and exploding my expansion bottle.
Car has been to 1320, now has a new supercharger (28k miles), a delivery miles cylinder head, new thermostat, expansion bottle, and the guys also kindly replaced my piston rings so those are brand spanking
I have to do 6-700 miles running in and then i've almost got a brand new engine