Every parking ticket slapped on a windscreen or handed to a driver by Islington traffic wardens over the past five years could be legally challenged, parking campaigners claim.

This could amount to hundreds of thousands of tickets, worth around £90million.

Islington Council insists there is nothing wrong with its tickets, but motorists’ campaigners say all parking tickets should be suspended while the matter is cleared up.

The leader of the Lib Dem opposition, Cllr Terry Stacy, wants an urgent investigation.

He said: “The council needs to do an immediate and independent review to reassure residents that tickets were issued correctly and are legally binding. If they are not, the council could be facing a massive bill.”

The claim centres on a ticket issued to 35-year-old Sai Wong for parking on a single yellow line in Chapel Market in December.

It has been overturned by the Parking and Traffic Appeals Service (PATAS) partly on the grounds of an allegedly missing clause in the ticket’s small print.

According to adjudicator Michael Lawrence, a few words relating to exactly how Mr Wong could appeal his £130 fine were missing – amounting to “procedural impropriety”.

This wording has been used on all Islington Council parking tickets issued directly to drivers, or placed on their windscreens, since April 1, 2008 – when the council was still in Lib-Dem hands.

This is likely to represent hundreds of thousands of tickets worth more than £90million – though tickets issued by post are not affected.

The council issued 701,474 parking tickets, worth £77.5million, between April 2008 and March 2012, and is likely to have issued around 150,000 more tickets, worth around £15million, during 2012/13 – though many drivers will have received a 50 per cent early-payment discount and others will have successfully appealed.

The council recently admitted that all traffic fines issued between November and April at the new Drayton Park width restriction in Highbury were invalid because the road signs did not match the associated traffic management order.

It agreed to pay back the 10,974 fines – worth £1.4million – to any motorists who contacted them.

Rupert Lipton, managing director of NMAG (National Motorists Action Group), said he expected “nothing more than a similar acceptance” in this case, adding that there was a “statutory review process” if the council disagreed with the adjudicator, but that “the decent and fair thing to do in the interim is to suspend enforcement of all penalty charge notices”.

Parking campaigner Albert Herbert, who represented Mr Wong, added: “In my opinion, any tickets issued with this wording should be paid back.”

Islington Council says its tickets are compliant with regulations and will not be cancelled.

A spokesman said its legal team had checked that the wording complied with national regulations. He added: “We are happy to check that the wording is as clearly phrased as possible, but our legal advice is clear that the wording complies with regulations.”

The council will also not challenge the adjudicator’s decision, claiming that one decision is not binding on another.