Livingstone pledge for 20mph London

He said the new restriction was aimed at further reducing road deaths and claimed that if Boris Johnson won the mayoral election on 1 May, the death toll would begin to rise again.

The Tory candidate has said he is opposed to a 20mph limit on London's residential streets.

Mr Livingstone told the annual conference for Roadpeace - the charity for road crash victims - that his road safety measures had led to a 40 per cent reduction in the number of people killed or seriously injured on roads every year.

He said: "The presumption on London streets should be 20 miles an hour with very rare exceptions. Boris Johnson's policies are completely and diametrically opposed to mine.

"I confess we have rephased traffic lights and done the outrageous thing of giving pedestrians an extra two seconds to cross the road.

"Boris Johnson has said he will rephase traffic lights so traffic flows more smoothly but 'smoothly' is actually a euphemism for faster."

Research has shown that nine out of 10 pedestrians will be killed if hit by a car travelling at 40mph, but only one in 20 will die if hit at 20mph.

Mr Livingstone said more pedestrian crossings and longer green man crossings had meant 500 fewer children were hurt or killed on the roads each year since 2000.

He added that if Mr Johnson were to become mayor all his hard work would be ruined. "If we go into reverse we will go back to a much more dangerous city and a much more unpleasant one," he said. "There is a very real chance... more people could die on London's streets."

In response, Mr Johnson said: "Road deaths are a tragedy and not to be used as political tools. The Mayor's comments are an insult to those who have lost loved ones in this way.

"These claims are absurd and ridiculous. If there were ever a demonstration that this Mayor has had his day and lost the plot, this is it."