The environment department (Defra) has decided to continue to allow residue from energy-from-waste plants to be sent to hazardous waste landfill sites.
The UK has been short of outlets for this type of waste, known as air pollution control residue, a fine powder that remains once gases have been cleaned.
For several years, the Environment Agency has allowed for it to be disposed at landfill if the waste exceeds the limits for leaching set by the 1999 EU Landfill Directive by up to three times.
In 2010, Defra pledged to withdraw the exemption. Since then, the waste industry has been working on technologies to recover the waste and use it in products, such as a replacement for aggregates in concrete.
Defra has now dropped plans to phase out the derogation over two years, citing a lack of alternative disposal solutions as the main reason. Jacob Hayler, executive director of waste trade body the Environmental Services Association, said the decision would damage investment in alternative treatment technologies.