Parliament Square Traffic lights

This morning just after 9 I was confused by the trafic lights at Parliament Square. As I apporoached the lights they were green, but nobody was moving. So I thought the police must be directing traffic (not short of Coppers around there - and had just past a couple directing a contraflow before the Square).

Anyway I filtered to the front and saw no Police so proceeded through the Green lights, but tons of traffic was coming from my left, so I reckon they had a Green signal at the same time