Buses in Oxford could have their emissions legally capped in a bid to cut pollution in the city.

Oxfordshire County Council has applied to Government to set a limit on nitrogen dioxide emissions as part of plans with Oxford City Council to make the city a Low Emissions Zone (LEZ).

The authority is the first in the country to propose setting the bar at the Euro 5 level – meaning buses can only produce two grams of nitrogen oxide per kilowatt hour. The average UK bus currently produces five grams.

Since 2009 bus operators have invested in low-emission buses, including diesel-electirc hybrid buses, leading to about a 60 per cent reduction in emissions.

But many older vehicles remain in use.

If agreed, the LEZ would mean all buses operating within the city will have to meet the highest ‘Euro 5’ standards.

Buses that do not meet the standard would have to be replaced or refitted with an exhaust treatment device.

And engines will also have to be switched off at bus stops when the bus is stationary for more than one minute.

Rodney Rose, Oxfordshire County Council’s cabinet member for transport, said: “Oxford is a beautiful city and we want the centre to be as attractive as possible for people to enjoy.

“Huge steps have already been taken to improve the air quality but there is still more that can be done.”

Oxford City Council is also looking at applying the same rules for taxis and licensed private hire vehicles.