Millions of toll payments for crossing the new Mersey Gateway Bridge may have to be refunded, a lawyer has said following a legal test case.
The Traffic Penalty Tribunal (TPT) found a driver was not liable to pay the £2 toll as Halton Council had not specified the fee correctly.
It also failed to give correct notice of charges on the £600m Runcorn to Widnes crossing, the TPT said.
Halton Council said it "strongly disputes" both points.
Ten million vehicles
Celebrity motoring lawyer Nick Freeman - who is nicknamed Mr Loophole - told the BBC he had examined the tribunal ruling and thinks the council will have to refund every fee charged since the bridge over the River Mersey opened in October.
Ten million vehicles have so far crossed the bridge over the River Mersey and 250,000 penalty charge notices have been issued for failing to pay the toll, according to Halton Council.
Motorists using the bridge can register for discounted charges, or pay online either in advance or by 23:59 BST the day after they cross.
Operators estimated £1m of fines had been issued in the first month.
The TPT said it was conducting a case review on 8 May of C v Halton Borough Council after ruling the authority had not made it clear it was £2 for cars to use the bridge, in the Mersey Gateway Road User Charging Scheme Order 2017, and that it had failed to give correct notice of toll charges.
It has also put 456 current penalty appeals on hold until the review.
'Banged to rights'
The council said it did not agree with the decision, saying its legal advisors had said it was "legally sound".
It has applied for the decision to be reviewed.
It said it was also updating its charging order to make charges clearer.
It said it was "business as usual on the Mersey Gateway" and motorists should continue to pay tolls or "run the risk" of penalty notices.
However, Mr Freeman said Halton Council was "banged to rights" as it had not advertised the tolls in a local paper.
"Councils are required to advertise these things in both the London Gazette and the relevant local paper. They failed to do this so due process was not followed," he said.