Rule 14 - The Highway Code

Parked vehicles. If you have to cross between parked vehicles, use the outside edges of the vehicles as if they were the kerb. Stop there and make sure you can see all around and that the traffic can see you. Make sure there is a gap between any parked vehicles on the other side, so you can reach the pavement. Never cross the road in front of, or behind, any vehicle with its engine running, especially a large vehicle, as the driver may not be able to see you.