Kiln three was ordered to close in March

Castle Cement in Padeswood was ordered to stop using one of its kilns in March following a breach of emission limits for dioxins.

The company said it had voluntarily suspended operations on kiln three until test results were available.

A new �60m kiln is due to open in June.

A spokesman for the Environment Agency said the investigations "are continuing".

New kiln

"It's a detailed thing and we're working with the company. The kiln remains closed."

He added that the investigation would take "as long as it takes".

The kiln was due to close shortly anyway to make way for the new fourth kiln which is expected to come into operation on a trial basis in June.

The kiln is designed to run on Cemfuel, a controversial concoction of waste solvents and chemicals - which protesters fear will pollute the environment.

However, the Environment Agency has issued a permit which demands strict controls on pollution.

Danny Coulston, general manager at the Padeswood plant said the company has voluntarily suspended operations on kiln three.

"We are still waiting for the agency to finish its investigation, but kiln three is now closed and we are waiting for kiln four to start," he said.

"Kiln four has been to built to reduce emissions at the site as well as increase production," he added.