Environmental consultants have been hired at a cost of £24,000 to examine the possibility of creating an exclusion zone around Oxford city centre to ban high- polluting traffic.

Oxford's air pollution problem is reported to be so bad that city council chiefs think a low emission zone (LEZ) is the only hope of cutting dirty air levels.

Harwell-based AEA Technology is undertaking the study, which would determine how a scheme could work and which vehicles could be banned.

UK National Air Quality Information data shows Oxford city centre has higher nitrogen dioxide levels than Reading, Bristol, Leamington Spa and Bath.

European air quality regulations dictate the level for nitrogen dioxide should not exceed 200 microgrammes per cubic metre for any single hour, and 40 as an average throughout the year.

Kerbside readings in Oxford city centre (St Aldate's) showed the highest reading last year was 246 and the average mean was 67.

Oxford City Council environmental protection officer Tony Payne said: "We are breaching European standards and actions are needed to reduce air pollution.

"Air quality is a serious issue and serious actions are needed to improve the quality of air to meet these European air directives.

"Unless actions are taken we are not going to meet them and the Government will be knocking on our door.

"There is a problem and this problem needs to be addressed urgently.

"We need the analysis to be carried out to identify the extent of the low emission zone and the restrictions that would need to go in to it, plus enforcement."

At the heart of the problem is the fact no one can say for sure how bad pollution in Oxford is, with the city council frequently clashing with the county council over the issue.

An LEZ in Oxford is unlikely to be in place for at least 18 months.

The consultant's study will take between six and nine months and an LEZ would require road traffic orders to be drafted, consultation to be carried out and final approval from transport secretary Alistair Darling's department.

County councillor David Robertson, cabinet member for transport, said: "We are working with the city council to minimise and reduce air quality issues in Oxford that's a requirement of us."

Nigel Eggleton, commercial director at Oxford Bus Company, said the firm supported "a deliverable LEZ".