The colour of the light is a moot point. If a driver is in charge of a vehicle that is on the road, then the laws apply. The UK government's guidance on this is

The colour of the light is a moot point. If a driver is in charge of a vehicle that is on the road, then the laws apply. The UK government's guidance on this is clear on that and after years of media & press about phone usage whilst driving, nobody in the UK can claim ignorance of the law. https://www.gov.uk/using-mobile-phones-when-driving-the-law https://www.gov.uk/using-mobile-phones-when-driving-the-law