Before you start to cross: look to the right for traffic.
Many tourists in London don't look the correct way when crossing the street, because they normally drive on the right. Effects of the automobile on societies...
In London you often find the warning "Look Right" painted on the street, like this in the picture.
Strisce e semafori a Londra (linguaggiomacchina.it)
Pedestrian crossing (wikipedia.org)
New Pedestrianism (wikipedia.org)