Mr Livingstone says he will work with all 33 boroughs on the speed limit

Ken Livingstone said he would work with all 33 boroughs to impose the restrictions in built-up areas.

According to the mayor, there has been a 40% drop in all road casualties in London in the last eight years.

In his transport manifesto for the mayoral election he pledged to improve this figure to 50% by 2010.

Mr Livingstone is battling for a third term in the mayoral elections on 1 May.

His transport plans include a �16bn cross-London Crossrail project and a �1bn a year Tube modernisation.

MAYORAL CANDIDATES Alan Craig Christian Peoples Alliance & The Christian Party Boris Johnson Conservative party Brian Paddick Liberal Democrat party Chris Prior Stop The Congestion Charge party Damian Hockney One London party Dennis Delderfield New Britain Gerard Batten UKIP Ken Livingstone Labour party Lindsey German Respect party Matt O'Connor English Democrats party Richard Barnbrook BNP Sian Berry Green party Winston McKenzie Independent

Speaking to residents and road safety campaigners in Kings Cross, central London, on Friday, he said: "Our success so far is the result of comprehensive policies to support pedestrians, including giving pedestrians longer to cross at traffic lights even if it means cars have to wait a few seconds longer.

"Research has shown that designating all residential streets as 20mph zones will make a huge difference to cutting further road casualties.

"Nine out of 10 pedestrians will be killed if hit by a car travelling at 40mph, two out of 10 at 30mph and one in 40 at 20mph."

According to the mayor, there are about 400 20mph zones in London.

He added that more 20mph zones will not mean more speed bumps and he said he is working with councils to replace the bumps with speed cameras and "other technological innovations".

Green Party mayoral candidate Sian Berry said: "I'm pleased that Ken Livingstone has taken on my policy of 20mph speed limits, but he appears to be taking a patchwork approach.

"Forcing drivers into a guessing game about whether a road counts as 'residential' or not would go some way to ruining the potential of a 20mph limit to save lives."

Liberal Democrat candidate Brian Paddick said: "Ken's claims to have improved road safety as a result of his actions is misleading.

"In fact, things like the 20mph speed limit are a matter for local authority over which the mayor has no control," he added.