Environmental bodies have warned the Government that the use of kerosene, creosote and red diesel to ignite the pyres is pumping lethal dioxins into the air.

There are also concerns that burying thousands of sheep in pits will pollute the water table. The Agriculture Secretary, Nick Brown, announced last night that cattle less than five years old will also be buried.

David Manning of Nanovapor Systems, which tackles pollution problems around the world said: 'We are storing up huge problems for our children and their children,'

As the crisis moves into its sixth week with no sign of abating, the environmental issue comes as a fresh headache for the Government. Yesterday Maff announced 51 more cases of foot and mouth on Friday, revealing that the rate of increase is not slowing down. The Government is now so concerned about the environmental issue it has launched an inquiry into the effects. The National Environmental Technology Centre has been asked to monitor the hundreds of pyres that have been filling the countryside with acrid smoke.

Last week in its first report to Michael Meacher, the Environment Minister, the centre said there was evidence of dangerous levels of dioxins entering the atmosphere, particularly in the 3km radius around the fires. Dioxins are among the most deadly pollutants. At minute concentrations in the air they can cause cancer, changes in the the body's genetic make-up and fertility problems.

Mike Childs, campaigns director of Friends of the Earth, said: 'The release of so many dioxins is especially of concern, given that dioxin exposure can lead to cancers, reduced fertility, genital malformations and learning difficulties.'

The Environment Agency said in a briefing document: 'Contamination of groundwater can be difficult to detect and difficult, sometimes impossible, to remedy.'

Tim Brown, the deputy secretary of the National Association for Clean Air, said: 'Coal and old sleepers covered in bitumen ... will produce a range of pollutants, including dioxins and polycyclic aromatic hydrocarbons, which are carcinogenic.'