Friends of the Earth has placed a register of Britain's most polluting factories, gasworks, chemical plants and refineries on the Internet.
The database covers 1,000 sites in England and Wales and is taken from the Government's pollution inspectorate's chemical releases inventory, first published last year.
Disused gasworks, such as the site at Beckton, east London, used in the film Full Metal Jacket, feature heavily, with more than 1,000 scattered around the country. Virtually all will be contaminated with substances used in the manufacture and purification of "town-gas" including various forms of cyanide, toxic heavy metals and phenolic compounds, some of which may be carcinogenic.
The sites became contaminated mainly through the purification plants which cleaned the gas. One of the worst contaminants is "Blue Billy", or spent oxide. This material, often dumped on site, absorbed most of the noxious components in the gas.
Beckton is one of the most contaminated sites. Part of it has been redeveloped as a housing estate while the remainder is still owned by British Gas.
Debbie Tomlin, who lives on part of the redeveloped site, says she, her husband and two children all suffered from illnesses and skin rashes caused by contamination. "We've had soil tests done in our own garden and at other places around the site. The bits that were contaminated they removed and they removed the soil from eight gardens," she said.
British Gas has made strenuous efforts to decontaminate the worst sites and reclaim the rest for housing and industry but they have been left frequently with a highly toxic legacy. They have done comprehensive surveys on most former gas works sites but refuse to reveal the results and claim it is commercially confidential information.
FoE hopes the new database will help force British Gas and other companies to reveal what they know about their land.
But Bob Bell, of SGS Environment, which advises local authorities and industry on decontaminating old gasworks, said he sympathised with British Gas's desire to keep information secret. "Morally its right to disclose the information but it's just going to scare people. You need experts that have the necessary perspective to deal with the information," he said.