Judith Hackett of the Chemical Industries Association: The chemical industry has a responsible care programme

Friends of the Earth claim more than 10,000 tonnes of carcinogens, or cancer-causing chemicals, were released into the air by British factories in 1996. Using official pollution data from the government's Environment Agency, the group's aim is to "crack down on the cancer carriers".

Senior Pollution Campaigner Mike Childs said: "The worst factories are being allowed to release a quite appalling amount of health-threatening pollution." The top polluter for 1996 - the latest year for which the figures are available - is Associated Octel Co Ltd in Ellesmere Port, Merseyside.

Children's health is thought to be at greater risk

During that year, the company released 5,340 tonnes of carcinogens, including lead, chloroethane and vinyl bromide. The most polluted part of Britain was the north-west, where 9,918 tonnes of carcinogens were released.

Call for action

Next on the list was the North-East, with 1,046 tonnes, and then the East and West Midlands with 936 tonnes. The South-East and London released 143 tonnes, and bottom of the list was the South-West with 90 tonnes.

Four ICI plants are also named - Runcorn, Middlesbrough, Redcar and Thornton-Cleveleys. Other companies in the top 20 include Shell, Albright & Wilson and Dow Chemicals.

Mr Childs said: "The government must take tougher enforcement action. And it must now deliver on its election pledge and publish comprehensive pollution inventories.

"Then we can all find which pollution sources are threatening our health." The chemical industry says it is doing all it can to reduce levels of pollution.

Children are thought to be at a greater risk than adults when exposed to pollution. A connection has been made between higher cancer rates and proximity to industrial locations. The research was carried out in Teesside and Birmingham.