Casualty rates at some speed camera sites have worsened since their installation, according to figures.

That includes the camera in Castle Hill in Parkstone, where there were three serious-injury and 11 slight-injury collisions in 2009 compared with only three serious and six slight at the spot in 2001, before it was put up.

Some schemes have reported a reduction in accidents and injuries, and overall the Department for Transport's figures show a mixed picture of the effectiveness of speed cameras.