Pollution in Brighton and Hove has reached dangerous new levels.

High concentrations of nitrogen dioxide identified in the city were found to be above the measures deemed safe by the Government.

Nitrogen dioxide can aggravate respiratory conditions such as asthma, bronchitis and dry coughs and can worsen eye, nose and throat irritations.

Levels of the gas and particulates - tiny particles which can be absorbed in the lungs - were found to be almost 50 per cent above the safety threshold figure.

The highest reading was found in Lewes Road, Brighton, taken at a monitoring station between Elm Grove and the Vogue Gyratory, which was 58 microgrammes per cubic metre, against a 40-microgramme target.

Other hot spots were identified at Preston Circus and Grand Parade.

Long-term exposure to nitrogen dioxide, chiefly the result of exhaust fumes from motor vehicles, can increase susceptibility to infections and to diseases such as influenza.

The cocktail effect, when it mixes with high levels of other pollutants, increases the risks to health.

Brighton and Hove was tested as part of a national assessment of air quality. Further testing confirmed nitrogen dioxide levels to be in breach of the safety threshold which comes into force at the end of next year.

Drastic action, including diverting traffic from the worst areas and introducing on-the-spot emissions tests, must be taken if Danger levels of pollution the city is to meet future targets.

Brighton and Hove City Council would be obliged to declare what is known as an Air Quality Management Area (AQMA) if the targets continued to be exceeded.

The council said the readings still had to be verified and it was too early to know what measures it would take to improve air quality.

If an AQMA was declared it could be any size, from individual streets to the entire city.

Diverting traffic away from the main routes into Brighton and Hove would be difficult because the Highways Agency is always reluctant to agree restrictions on major roads.

The council would, however, have the power to test vehicle emissions at the roadside and issue on-the-spot fines to offending drivers.

Green Party councillor Simon Williams said: "Only a sustained reduction in private road traffic entering the city, alongside investment in public transport, will cut urban pollution in the long term."

Judith Macho, the council's assistant director of public safety, said:

"What we really don't want to do is scaremonger because this is not something to panic about.

"Generally, air quality is improving across the city. It is just this one area with this one pollutant we are looking at in a bit more detail.