Hundreds of buses running in Sheffield do not meet the emissions standards for the city’s Clean Air Zone as they have been retrofitted with faulty technology, MPs were told.

The diesel buses were retrofitted with devices designed to reduce harmful nitrogen dioxide emissions, as part of a programme funded by the Department of Transport.

It began after the government ordered Sheffield City Council to set up a Clean Air Zone. Launched in February, the scheme charges owners of the worst-polluting heavy goods vehicles, vans, buses and taxis a daily fee if they are driven in a designated area of the city.

But Paul Blomfield, MP for Sheffield Central, said the exhausts “don’t reach the required temperature” for the catalytic reduction technology to work effectively, as the buses have to stop regularly in built-up areas of the city.

Sheffield Clean Air Zone - charges for the first eight months totalled almost £3.3m

The Labour MP said around 75 per cent of the 400 buses in Sheffield have been retrofitted but most still do not comply with Euro 6 emission standards.

During a debate in Parliament, he said it is “pretty clear” that retrofitting has failed and the buses need to be replaced with battery or hydrogen-powered vehicles.

“Retrofitting will not be a suitable way of mitigating emission from buses and alternative solutions will be required. We need those solutions and that means replacement buses,” Mr Blomfield said.

He told MPs the government must provide Sheffield City Council with funding to buy greener buses, during the second round of its Zero Emission Bus Regional Areas (ZEBRA) scheme.

During the debate, Anthony Browne, Minister Decarbonisation of Transport, admitted the retrofitting project has been “troubled”.

“It hasn’t performed as we expected,” he said. “We are analysing exactly what the impact is and what the mitigations can be. We will publish those results soon.”

He added: “The retrofitting programme is only ever going to be an interim scheme. The ultimate long-term ambition is to go to zero emission buses.”

Mr Browne said the government committed to providing funding for 4,000 zero emission buses in its National Bus Strategy in 2020, and more than 1,600 are already on the road.

He said South Yorkshire received 27 zero emission buses as part of the first round of the ZEBRA scheme, and local authorities can now apply for a share of £129m in the second round.

Sheffield buses fitted with faulty technology that is 'failing' to cut pollution