Bus company Stagecoach has been criticised for not doing enough to help cut pollution in Oxford -- while its main rival has been praised.

A Stagecoach bus in the centre of Oxford

Environment experts at Oxford City Council said Stagecoach could do more to cut high levels of smog-causing nitrogen dioxide.

Oxford Bus Company was praised for introducing a fleet of low-emission buses and urging drivers to turn off their engines while parked.

The comparisons were made during a meeting of the council's executive board on Monday, September 1, to discuss how to improve air quality.

Roger Pitman, of the council's environmental health department, said annual emission levels in many Oxford streets would fail to meet national targets by 2005 unless action was taken.

In Queen Street, George Street and High Street, emissions would have to be almost halved if the recommended level was to be achieved.

Mr Pitman said he believed that buses stopping and travelling at slow speeds were the most significant source of nitrogen dioxide. He said: "Present measures are not working. The Oxford Transport Strategy has not helped cut pollution. Oxford Bus Company has done so much voluntarily to make its service more environmentally-friendly.

"Stagecoach is slowly trying to help, but has so far done very little."

Stagecoach spokesman David Whitley said the company had invested £20m in 150 new buses since 1997, each of which exceeded European Union emissions guidelines, and a further 10 vehicles were expected to join the fleet in the near future.

He said: "We take our responsibilities very seriously and I hope our investment in new, low-emission vehicles helps prove this."

Mr Pitman wants all bus companies to consider fitting devices to vehicles to cut nitrogen dioxide emissions by 30 to 40 per cent. Each device costs £6,000. Grants of up to 75 per cent of the cost are available from the Energy Saving Trust.

The 1995 Environment Act requires councils to review air quality. In 2001, a study found that Oxford was likely to have higher nitrogen dioxide levels than national targets by the end of 2005.

The city was declared an Air Quality Management Area. The city and county councils agreed to work together to tackle the problem.

It is estimated it will cost about £90,000 to monitor emissions until 2010.