Green London Assembly member Jenny Jones, who was knocked off her bike at Elephant and Castle roundabout - a major blackspot - last July, said: "This is a very useful tool." But she added that a lot of accidents were never reported to police. "I think what you are seeing is the tip of the iceberg. I was knocked off by a car and broke my wrist, but stupidly didn't report it at the time." Her arm was in plaster for six weeks, and she still suffers pain.