Concern about rising numbers of speed cameras is "perfectly understandable" but they are playing a real role in saving lives, Tony Blair has said.
The spread of electronic speed enforcement has been controversial
The prime minister told MPs cameras in accident hotspots prevented about 900 deaths and serious injuries a year.
Labour's Patrick Hall urged the PM to expand the programme of speed cameras and road safety measures claiming they had reduced deaths and injuries by 35%.
Mr Blair said a "balanced policy" was the best approach.
Earlier this week a government study claimed speed cameras saved 100 lives every year.
The three-year study of accident rates on roads with cameras shows a 40% cut in the number of people killed and seriously injured.
The number of cameras in England and Wales is growing. There are now around 5,000 fixed speed cameras and sites where mobile cameras are often located.
Asked to back calls for an expansion in the camera programme during prime minister's questions, Mr Blair said: "It's important that we use speed cameras where it's clear there's a proven benefit to the safety of motorists and others in doing so ...
"There is obviously concern, for perfectly understandable reasons, about the use of speed cameras.
"Nonetheless, I think the reduction in deaths has been somewhere in the region of almost 900 in a year as a result of the introduction of speed cameras in places where they do have accident hotspots."
Downing Street later said Mr Blair was referring to figures suggesting the cameras cut 870 deaths and serious injuries a year.