Happened on the way back during the pretty heavy slush that was going on up the M40
I stopped to get fuel (this time the pre-crash detection was off as well!), looked at the badge where the sensors are and there was a perfect disc of ice (as well as the entire grill and number plate!)
Headlights were caked in ice/slush as well so gave it a going over before getting my wallet emptied by motorway services petrol and all was working once again.
I should have taken a picture of the perfect disc of ice over the badge as it was rather amusing - made me wonder what happens to ES owners in countries with permanent weather like yesterday