A sewage treatment works is to undergo a £6m expansion after years of being used well above capacity.

Northumbrian Water yesterday announced that by 2007 the plant at Middleton St George will be big enough to cope with waste from the village and the redeveloped Durham Tees Valley Airport.

The announcement comes as Middleton St George's leading councillor branded the existing sewage works a disgrace and a public health hazard.

Parish council chairwoman and Darlington Borough Councillor Doris Jones said raw sewage was spilling out across the fields and into the river, generating an unbearable stench during spells of hot weather for those living close to the works on Middleton One Row.

She said that tankers travelling from the site were also leaving trails of waste on the roads and verges.

"It is particularly bad along Hill Rise and it smells appalling. It really is a health hazard - it is all over the road," she said.

With the population of Middleton St George rising from 1,800 to 5,000 in eight years, Coun Jones said the sewage system was being used beyond its capacity.

Ron Dawson, who lives on The Front, said he was shocked that the treatment plant could be in such a worrying state.

"There are 100 or so houses being built in the village at the moment and yet the sewage works are already not coping," he said.

Alistair Baker, of Northumbrian Water, said the works had been designed years ago to cope with considerably less waste than at present.

He said temporary measures had been taken, including installing a sand filter, to handle the extra sewage and to prevent pollution of the river. Sealed tankers also carry sludge from the site to the regional treatment centre, at the mouth of the River Tees.

A spokesperson from Darlington Borough Council said new developments in Middleton St George were being built with holding tanks, which pump sewage to the treatment works at off-peak times.