Who would have the burden of proof, you (driver) to prove that you were not on a business journey or the other parties insurance to prove you were. In my specific instance, I have to drive past the train station that I use to get to my normal place of work. So unless I was actually coming in our out of the station car park how would anyone know? Although if I was on the way to the airport to take a flight to the US which I also do once a year that maybe different, but as I work in the private sector, they do not pay me mileage nor am I on company time, although they do pay for the flights.
Let's ignore the Police because they won't care as long as there is 'some' insurance on the vehicle.