Levels of a toxic gas at Gatwick are almost twice the amount recommended by the European Union.

A survey by the Chartered Society of Physiotherapy has revealed Gatwick to be among the four worst polluted airports in Britain.

Roadside tests revealed 60 to 70mg of nitrogen dioxide per cubic metre near the airport, far above the EU's recommended limit of 40.

Nitrogen dioxide is a brown hazy gas that can be seen hovering over most towns and cities during hot summer days.

It aggravates asthma, increases allergies and makes it harder for lungs to function. It also hurts plants, making their leaves die.

The fumes are emitted by cars travelling to and from the airport, by aircraft and by traffic on the nearby M23 and A23 roads.

Dr Mark Britton, of the British Lung Foundation, said people with chest complaints could feel ill when visiting the airport as a result of the pollution.

He said: "Exposure to fumes could exacerbate underlying lung conditions such as asthma."

He called on the airport's owner and operator BAA to bring emissions in line with the EU's limit.

The data was collected by the Department for Environment, Food and Rural Affairs in 2003, the same year readings of 58 mg per cubic metre were recorded in Lewes Road, Brighton.

But the next set of statistics are expected to show a slight decline.

Peter Barclay, of the Gatwick Area Conservation Campaign, said few people living near the airport realised how much pollution was on their doorsteps.

He said much of the pollution was blown to the north east of the airport by a south-westerly prevailing wind.

He said: "We don't get many complaints but people aren't aware of the pollution. Children go to school and get coughs and colds and it sometimes takes parents years to learn that these are not ordinary viruses that children pick up, they are a result of the environment they are living in."

The Transport and General Workers Union, which represents many of Gatwick's 25,000 employees, is to call on BAA and councils near the airport to take action to curb pollution.

Chris Todd, of Brighton and Hove and Mid Sussex Friends of the Earth, said: "This is a serious issue for the people working at Gatwick and another reason why we need to curb expansion in the aviation industry."

A Gatwick spokeswoman said the report was "misleading" and failed to take account of the amount of pollution generated by traffic on the A23 and M23.