Oxford city centre has the worst air pollution in the country, according to a survey which compares inhaling the air there to smoking 61 cigarettes a day.

Craig Simmons with 61 cigarettes Nitrogen dioxide levels in Queen Street are almost twice the Government limit, says a study by gas company Calor.

Levels of nitrogen dioxide were compared to the amounts of the damaging chemical inhaled from a cigarette.

Oxford topped a table of UK towns and cities. Bath came second with pollution equivalent to smoking 46 cigarettes per day.

Calor compiled the table after analysing statistics for 30 places in the UK.

Green city councillor Craig Simmons said: "For the sake of the health of the people of Oxford and our environment, the city and county councils must act now to reduce air pollution in the city centre."

Calor spokesman Andrew Ford said: "Poor air quality is a clear and present danger in Oxford here and now."

Cancer Research UK spokesman Martin McGlown, based at Oxford Business Park, said: "We would be interested to discover what methodology Calor used to equate spending a day in Oxford city centre to smoking three packets of cigarettes.

"We certainly would not want people to come away with the impression that spending a day out in Oxford is just as bad as smoking 60 cigarettes."

Mr Ford called on councils to encourage the use of cleaner fuels.

THE CALCULATIONS EXPLAINED: Calor took local authority air quality measurements from city centre locations.

Calor's calculations were based on taking the annual average nitrogen dioxide level in a day and translating this into the amount of nitrogen dioxide inhaled by an adult at rest -- an average of six litres of air per minute. This was then compared with a Rothman's Light cigarette, which produces a stated 29mg of nitrogen dioxide, to calculate how many minutes of breathing at that location, on average, would equate to one cigarette.