Its a defined area to pass across the road. The UK doesn't have J walking laws, once a pedestrian steps out to cross the road in front, priority changes in favour of the pedestrian, you wouldn't want to mow them down. For insurance and police, if someone literally stepped out in front of your car travelling along the road, and you had no time to stop, you would not be at fault. The pedestrian has been negligent in their actions, but legally pedestrians have priority over vehicles. It should be that way, it offers some protection to all vulnerable road users.
Rule 170 of the Highway Code advises that if a pedestrian has already started to cross the side road into which you’re turning from a main road, you must give way to them