Clean air zones could deliver £6.5bn of economic returns but only if polluting private cars are banned and the government boosts its funding for the schemes, according to research commissioned by a group of council leaders.

An analysis carried out by financial consultants CEPA on behalf of UK100, which represent 14 mayors and city leaders, found that a Class D CAZ - the only option to include polluting private cars - could see up to £4.30 returned for every £1 invested into the scheme.

In comparison Class A, B and C CAZs, which exclude private cars,  offer no more than an 80p return for every £1 spent. The methodology for calculating the economic benefits of cleaner urban air is based on a 'notional' CAZ analysed using the DfT's WebTAG traffic tool and modelling methods developed by economic consultants CEPA. The £6.5bn return is the maximum of a range of outputs based on a £1.5bn additional investment in up to 60 CAZs across the UK.

Benefits include reducing congestion, improving air quality, reducing health costs, reductions in accidents and wear and tear on roads. These are all offset by the cost of any scrappage scheme, electric vehicle recharging infrastructure and a reduction in tax revenues from diesel and petrol sales.

None of the councils currently in the process of introducing a CAZ have opted to introduce a ban on polluting cars, known as the Class D option, preferring instead to target non-Euro-6 HGVs, buses and polluting taxis. The option has been rejected by councils on the grounds that it penalises low income homes and would require expensive scrappage schemes.

Now UK100 members, which include London mayor Sadiq Khan, Andy Burnham, the mayor of Greater Manchester and Tim Bowles, the Conservative mayor of the West of England Combined Authority, are calling on chancellor Sajid Javid to boost the Clean Air Fund (CAF), which supports CAZ schemes, with £1bn of extra funding in this week's autumn spending round.

The additional funding would help cover the extra costs Class D CAZs could incur in terms of scrappage schemes and help fund up to 20 more CAZ schemes on top of the 60 already in the pipeline, according to the analysis.

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The CEPA report states: “As private cars often account for a large proportion of NO2 in the air - for example, 40% in Bristol - their inclusion in the CAZ restrictions often strengthens the strategic and economic case for a CAZ supported by an enhanced Clean Air Fund.

“The effect on individuals of including cars may be high, which may weaken the strategic case for a Class D CAZ ,which is the only class to include private cars.

“Where cities are struggling to achieve residents’ support for including certain types of vehicles in the CAZ, the CAF can play an important role in mitigating the negative impact of the CAZ while assisting groups who might otherwise find it difficult to achieve compliance.”

Polly Billington, director of UK100, said: "Cleaning up the air in our towns and cities makes sound economic sense and this study demonstrates that. It will boost the health of our communities and save the NHS money."