© PA Some private car park fines may be illegal, according to the RAC
Drivers could get refunds totalling tens of millions of pounds over "illegal" parking fines on private land.
The group claims "fines" of up to £100 for infringing conditions in private car parks may be illegal, and is calling on the Government to stop the practice.
Professor Stephen Glaister, director of the RAC Foundation, said: "Millions of drivers could be in line for a refund. We estimate that in 2013 alone, drivers might have been overcharged by some £100m."
Clamping on private land was outlawed by the Protection of Freedoms Act 2012, but charges for infringements of private car park conditions have grown to an estimated £100m per year.
Barrister John de Waal QC argues that this is likely to be several times more than compensation for a genuine loss, and would not be enforceable by the courts.
"They should be seen by the courts as penalties, which means they are unenforceable," he said.
Pauline Welsh, 57, was charged £60 after parking on what she thought was council-owned land - meaning it would have been free during the evening.
"It's shocking, and it needs sorting," the retired teacher told Sky News. "It's just not fair."
Mrs Welsh's husband, Alastair, appealed against her ticket - and another incurred by their son elsewhere. Both were overturned.
Figures from the British Parking Association show motorists won 49% of the 57,500 appeals made every year on average.
Professor Glaister called on the Government to set out what a reasonable charge should be.
"They allowed a system of ticketing to emerge which is barely regulated. In effect, drivers have been short-changed," he added.