Oxford councillors have pledged to seek powers which will allow them to fine bus drivers for leaving their engines running while waiting at city centre stops.

Earlier this month, Jean Fooks, chairman of the city council's environment scrutiny committee, proposed the move, together with Labour councillor Roy Darke.

To their surprise, the Oxford Bus Company and Stagecoach both said they would support the move, as part of a bid to improve air quality in the city centre.

Mary Clarkson, the council's executive member for the environment, has instructed officers to investigate the necessary legal steps. She said: "Not enough is being done to improve air quality, and we will bring a paper on these proposals to the executive. I have already asked officers to look into this.

"We will continue to talk to the county council because although we could enforce this on our own, it would be better to have the support of the county."

South Oxfordshire District Council adopted the necessary powers in 2002, but has yet to issue a fine.

At present, the city and county councils ask bus companies to urge drivers not to leave their engines running but there is little or no enforcement. The level of nitrogen dioxide in Queen Street is almost twice the Government limit, and is also too high in other parts of the centre to meet targets in the National Air Quality Management Strategy.

Nitrogen dioxide, contained in exhaust fumes, is less harmful than carbon monoxide, but can cause asthma if inhaled in sufficient quantities.

Under new traffic emission regulations, drivers could be issued a £20 on-the-spot fine by environmental health officers.

City and county councillors meet in a joint working group which has been established to improve air quality.

If plans to redevelop the Westgate Centre go ahead, new bus stops could allow Queen Street to become bus-free.