The council is owed more than three-quarters of a million pounds in unpaid LEZ fines.

Enforcement of Phase Two of the Low Emission Zone began in June this year.

Since then, more than 20,000 fines have been issued.

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In the first four months, from June to September, the council has confirmed it has recovered £478,560 and is owed £830,070.

The Glasgow Times revealed how hundreds of drivers have been fined multiple times, with the fines doubling with each breach.

Fines start at £60 – reduced to £30 if paid within two weeks- and can rise to a maximum of £480 for cars and £960 for coaches, HGVs and minibuses.

The figures show the council is owed more than it has recovered and drivers are warned the face debt recovery action if they do not pay the fine.

In Glasgow, the LEZ operated on a fine basis for those vehicles which do not comply if they enter the zone.

Other cities, such as in England, impose a charge, which allows vehicles to enter.

Diesel cars which do not meet the Euro 6 emissions standard and petrol cars that do not meet Euro 4 are banned from the zone.

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It means generally, diesel cars before September 2015 and petrol cars before 2006 are not allowed to enter the zone which is the city centre.

Road signs are posted around the zone warning drivers they are about to enter.

It is from the River Clyde in the South to the M8 in the west and north and High Street/Saltmarket in the east.

A spokesperson for Glasgow City Council, said: “Penalties are reduced by 50% if paid within 14 days, with all revenue above that incurred in running Glasgow’s LEZ scheme itself, only used for activities that help reduce air pollution or contribute toward achieving our climate change targets.

“These penalties carry additional charges if not paid or contested promptly, and if they remain unpaid would ultimately end up with our debt recovery agent for further action."