Road casualties in 20mph zones increased by almost a quarter in 2011, according to official figures.
The number of people killed or injured on roads in built up areas with a speed limit of 20mph totalled 2,262 in 2011, up by 24% from 2010.
Meanwhile casualties on 30mph roads were down by 1% from 2010, recorded at 125,494 in 2011, according to data from the Department of Transport.
Councils have been given powers to set 20mph zones in a bid to improve road safety.
Local transport minister Norman Baker said local authorities were best placed to make the decision on whether or not to impose 20mph limits in certain areas.
He said: "British Medical Journal research has shown a reduction in casualties and collision of around 40%, a reduction in children killed or seriously injured of 50% and reduction in casualties among cyclists by 17%.
"That is why we believe 20mph speed limits are useful in certain residential areas and support their introduction where it can be shown that they benefit road safety and quality of life."
He added: "It's vital that speed limits are suitable for local conditions and councils are best placed to determine what these limits are, based on local knowledge and the views of the community.
"Authorities up and down the country have been concluding that 20mph limits are indeed beneficial to their local areas."