No decision has been taken on the idea of making speeding motorists pay £5 to a fund to compensate victims of crime, Prime Minister Tony Blair has said.
Speed cameras have become a hot political issue
On a phone-in on LBC radio, Mr Blair promised to listen to people's views about the controversial new proposal.
But he argued a way had to be found to compensate victims of crime whose perpetrators were never found.
The Conservatives and motoring organisations denounced the idea as illogical and counter-productive.
Under the proposal, motorists given a prison term or suspended sentence would pay £30 to a Home Office fund providing victim and witness compensation and support.
Those fined for speeding or driving without insurance would face a levy of £5 or £10 under the government plan.
The plan, published on Monday, is one of several proposed changes to the funding of victim support services.
It is now going out to consultation.
During the phone-in, caller Kate from Holloway in London,said it was unacceptable for one person who had broken the law to pay compensation for somebody else's crime.
Mr Blair told her: "The decisions have not been taken yet and we are obviously going to listen carefully to what people say...
"Plainly in principle it is right that the criminal should pay the compensation to the victim.
"The problem is that in the circumstances where you get a crime where you either cannot identify or convict a criminal or you simply do not know how that person came about being injured, for example.
"It could be in a hit and run accident. You know it was a crime but you do not know who did it.
"In those circumstances the public pays compensation to that person. You cannot get the compensation from the criminal because you do not have someone who is actually convicted.
"The question is how do you fund such a scheme."
Mr Blair said there was also merit in docking the pay and benefits of people who refused to pay compensation, although some would argue it pushed families into further poverty.
Tories said the speeding levy measure would unfairly target minor offenders while leaving "real criminals laughing all the way to the bank".
Shadow home secretary David Davis said: "This counterproductive scheme will penalise minor
traffic offenders who have nothing to do with bringing
misery to the victims of serious crimes.
"This government has found someone else to pay for their actions."
Andrew Howard of the AA told BBC News it would be yet another cost "dumped on top of" drivers.
The RAC said the government was likely to alienate the normally law-abiding majority whose support it most needed.
Anthony Forsyth of Victim Support said that while the charity supported moves to improve services it was "uncomfortable" with the use of income from fines.
"Our position has always been that services for victims should come out of core [government] funding," he said.
"We are uncomfortable with the idea of linking this extra income with these sorts of minor offences."
Most of the proposals would apply in England and Wales only.
Publishing the consultation paper, Home Secretary David Blunkett said the current lump sum of compensation did not enable the government to provide the wide range of support victims needed.
Parking fines would be exempt from the new levy.
Other on-the-spot fines, such as being drunk in public or making a hoax 999 call, would also carry the extra charge.
The surcharges would raise £28m a year if they were all collected, but with an expected 60% enforcement rate they would raise just under £17m, the Home Office paper said.