Fines are said to have been levied despite incorrect road markings and on parking bays which are too small.

The Department for Transport said it expected councils to seriously consider repayment of illegal fines.

A council's spokesman said refunds may not be the best use of public money "where no-one was genuinely misled".

A councillor has highlighted one north London authority's past activities, which he described as "highway robbery". Alan Stanton, Labour councillor in Haringey, said the borough ticketed two yellow box junctions in Tottenham, north London, which were found to be unlawful.

"We have taken £120,000 from people we had no right to take," he said.

Haringey council said that when it discovered the boxes were illegal it stopped enforcing them and gave refunds to motorists who appealed.

The BBC has also discovered the entrance to a bus and tram lane which was incorrectly marked has earned Sheffield City Council £350,000, according to Freedom of Information figures.

Meanwhile, London Borough of Camden collected over £245,000 from drivers for who drove down a pedestrian's street which a ruling found was signposted unclearly.

According to barrister Oliver Mishcon, who specialises in motoring cases, local authorities have been acting unlawfully.

He told the BBC: "It's definitely a massive problem, definitely on a national scale, and we're talking about councils making tens of millions of pounds.

"From a legal point of view, the term is unjust enrichment. And if the council unjustly enriches itself, it's got to pay the money back."

Figures show that last year 60% of all appeals outside London were successful: 32% were not contested by councils and 28% were won by motorists. In London in the year to March 2007, 68% of appeals were successful.