But the agency has not ruled out taking legal action against Welbeck landfill site, which breached its permit four times in 12 months.

A report 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 another report from September 2007 said measures were ‘woefully inadequate’ to deal with the problem.

Action group Residents Against Toxic Scheme (RATS) claimed nothing had been done to stop the gas escaping in the past 12 months.

This week the Environment Agency said site operators Welbeck Waste Management LTD (WWML) had committed to a £250,000 investment to improve gas management.

Officers said 45 new gas extraction wells were being installed and new ‘gas flare’ should increase gas treatment by 66 per cent. But they warned that the expanding size of the tip meant extra measures would be needed over time.

An Environment Agency spokesperson said: “The installation of extra collection and treatment capacity is a major achievement that will help reduce future landfill gas emissions from the site.

“It is important to remember that a gas management system needs to develop as the site grows. We will continue our work to ensure that the gas management system develops as required to minimise landfill gas emissions from the site.

“Our legal team are currently reviewing the situation regarding breaches of the PPC permit. We cannot comment further on this at this time.”