The council could have issued hundreds of unlawful parking tickets, an investigation has revealed.

When a council suspends parking in an area, usually so roadworks or building can take place, the Department for Transport (DfT) says it needs to approve the signs advertising the suspension.

But Sutton Council, along with 15 other London councils, has not got DfT approval for the signs meaning any tickets issued in areas where parking has been suspended could be overturned - in the same way a Camden woman had a ticket overturned in 2010.

It is thought the revelation could lead to thousands of parking tickets across the capital being overturned but Sutton Council claims a subsequent judgement makes the tickets enforceable.

A BBC investigation revealed Sutton is among the councils not to have DfT approval for its signs. The council was asked, through a Freedom of Information request, for figures on how many tickets have been issued in suspended zones but Sutton was one of three councils not to supply the information on the grounds it would have taken too long to compile.

However Sutton Council is following advice from London Councils which says no legal precedent can be set by a parking appeal but an appeal since the case in Camden was unsuccessful on the grounds that signs were clear, regardless of whether they were DfT approved.

Paul Pearson, spokesman for campaign group www.penaltychargenotice.co.uk, says councils should refund tickets where non-DfT-approved signs were in place.

He added: "Many motorists are confused by suspensions and using unlawful signage does not help. When a motorist makes a mistake they receive a hefty fine from the council so it seems only fair that when a council makes a mistake they refund any money unlawfully taken."

Sutton Conservative Councillor Tony Shields said: "I think we should have DfT approval - they're the rules we all play by. A desire to bash the motorist runs through Sutton's Liberal Democrat council like DNA."