Grey plaque scheme highlights NO2 pollution in London

London's Choking initiative aims to draw attention to areas where nitrogen dioxide pollution threatens public health

They take their inspiration from the well-known signs linking people from the past with the buildings they once inhabited, but the symbols now appearing across London are to highlight a different connection.

In the past week, grey plaques - direct copies of the English Heritage blue plaques identifying the homes of the dead and famous - have been put up on buildings across the capital to identify streets and houses in areas where air pollution threatens public health.