Carbon dioxide and methane produced by Welbeck landfill site, which build up naturally when household waste decays, should be burnt off through a system of 'flares'.

But a report by government watchdog the Environment Agency (EA) from December 2006 said: "It is apparent that uncontrolled gas emissions from the site may be making a significant contribution to the UK's carbon emissions".

And three further reports highlighted breaches of the site permit because of gas emissions. One, from September 7, said measures were 'woefully inadequate' to deal with the problem.

Environmental group Residents Against Toxic Scheme (RATS) also released photographs which showed damaged gas piping at Welbeck bound together with gaffer tape.

The EA did not rule out prosecuting tip operator Welbeck Waste Management Ltd (WWML) for the gas emissions at the time, but has now decided against it.

Simon Firth, acting area environment manager, said: "We have thoroughly considered our response to the breaches that we have recorded at Welbeck. Breaches of a permit condition do not necessarily lead to a     prosecution."

The EA is still investigating an incident in February in which gallons of diesel spilled into the River Calder from the Altofts tip.

Mr Firth said: "A case file has been prepared on the diesel spill and has been sent to our legal team for review. We cannot comment further on this at this stage."