There is a story (isn't there always with a glimpseoflondon?) relating to these unusual traffic lights.
Created by French Sculptor Pierre Viviant it originally sat on a roundabout near Canary Wharf, part of the old Docklands area that now is largely banks and apartments. The sculpture was to represent the old plane tree that once stood in its place but was killed by pollution. It was originally intended that the lights would operate in a way that reflected the activity of the stock exchange. That idea was quickly scarpered when motorists became confused thinking it was to direct the traffic.
In 2011 major road works required the traffic light tree to be removed. A new place was sought for this very popular art work. Following all the usual bureaucracy a new roundabout was found and in January 2014 it was unveiled at the entrance to the Billingsgate Fish Market.