Well, went to see the stealer yesterday, wasted an hour or so sitting around, only for them to claim that the sensors' batteries had died!
My remonstrations regarding the extremely fortuitous (for them) situation that all 4 sensors chose the exact moment that the car was with them for balancing / a/c work to fail were completely ignored. It will now be very interesting when it comes time to change the tyres to see whether said sensors are still present or whether they removed them to simplify the wheel balancing (which was apparently very tricky).
NOT Happy!