The National Trust has warned government plans to build new runways at Stansted airport could damage a scientifically important Essex forest.

The trust has announced it will oppose the any such proposals because of concern about the impact on the local and national environment.

It is particularly concerned about Hatfield Forest, directly south of the airport, which is said to be the last remaining intact medieval hunting forest in Europe.

The forest is a national nature reserve and a Site of Special Scientific Interest (SSSI).

Nitrogen levels

Vikki Forbes, the property manager for Hatfield Forest, said: "We are only just beginning to understand what effect air pollution from aircraft and the associated car traffic may have on the growth of the trees, many of which are more than 500 years old."

Ms Forbes said background nitrogen levels in the forest were already at the recommended limit, and further development at Stansted could raise them to dangerous amounts.

She said the trust had been in discussion for two years with the airport to agree a programme of research into the impact air traffic has on the woodland.

"The forest is a wonderful site both for nature conservation and the local community.

"It is already badly affected by noise."

UK holidays

Peter Griffith, the National Trust's regional director for East Anglia, said: "In our response to government, we will be calling for a truly sustainable national aviation strategy."

He added the trust will also call on the government to promote the UK tourist industry to encourage people to take holidays at home.

The government's proposals to build one, two or three extra runways at Stansted have met fierce local opposition.

The consultation period ends on 30 November.