Good news, Hunters have fixed the problem. It was a software issue which was cured by doing a factory re-boot. The link between the radio and the parking sensors is that the 'beep' is played through the radio. Thus if the radio is dead the sensors don't sound!
They also did a software upgrade which cures the intermittent problem of the radio not turning off.
It has also improved the clock by making it visible without the radio being turned on, which it wasn't before.