Highway Code Rule 155

Single-track roads. These are only wide enough for one vehicle. They may have special passing places. If you see a vehicle coming towards you, or the driver behind wants to overtake, pull into a passing place on your left, or wait opposite a passing place on your right. Give way to road users coming uphill whenever you can. If necessary, reverse until you reach a passing place to let the other vehicle pass. Slow down when passing pedestrians, cyclists and horse riders.