There is a cycle traffic light (smaller version than the road variety ) at the Strand end of Waterloo bridge. Its at the end of cycle path and you have wait for light to turn green to cross the busy strand / waterloo junction. All the other traffic will wait. It the only one I know that exist.
One day I stopped for the light to turn green and there was another cyclist ahead of me waiting for the change. 2 coppers comes along and one of them approaches the first cyclist and demands to know what he is doing on the pedestrian path. We pointed to the big cycle mark on the road and the traffic light which also had a cycle mark. His faced turned green. The light also turned green and we both headed onto Waterloo Bridge.