Plans to charge to use city roads were shelved more than 30 years before London's congestion charge came into force, newly-released documents show.
Edward Heath's government considered a 50p charge for drivers
Edward Heath's government considered putting a "black box" in cars but there were doubts about the technology and whether offenders could be traced.
Files released by the National Archives show a 50p charge to drive into British cities was considered in 1971.
A £5 charge to drive into central London was introduced in February 2003.
London mayor Ken Livingstone risked his political reputation on the charge - two years later he is confident enough in the scheme to propose extending the zone.
But 32 years earlier, officials warned it would be impossible to trace offenders in the "Ealing jungle".
"We should, I think, have to be a far more tightly organised and regimented society than we look like being in the 1980s for a scheme like this to be practicable," one official warned.
He also said that ministers would risk being called swindlers if they put up road taxes after road charging was introduced.