Beddington incinerator, which serves four south London councils, faces enforcement from the Environment Agency after exceeding air pollution limits on 916 occasions.

The offences, which occurred between 2022 and 2024 at the energy-from-waste plant, were revealed last week after the operator Viridor admitted it had been collecting pollution data incorrectly.

Sutton Council, who sends waste to the site, has written to the Environment Secretary Steve Reed urging him to take enforcement action and say it was only told about the breaches 16 months after they were discovered.

A Viridor spokesperson said it takes environmental responsibility seriously and the under-reporting was “human error”.

The plant provides waste disposal services for 400,000 households across four councils – Croydon, Sutton, Merton and Kingston.

In order to operate, it has to record daily air pollution from burning the waste for key pollutants and ensure these remain below certain levels.

In March, Viridor realised that its monitoring software was incorrectly calibrated and that a reassessment revealed it had been breached daily pollution limits for nitrogen oxides regularly between August 2022 and March 2024.

The Environment Agency (EA) was notified and a subsequent investigation confirmed 16 breaches of its licence – one for each quarter across its two incinerators. The regulator told the BBC it was considering further enforcement action.

This could include a fine and, as a last resort, criminal proceedings – although such action is rarely taken.

A Viridor spokesperson said: “The Environment Agency has acknowledged the breaches at Beddington resulted from human error on the part of the third-party contractor, corroborating the independent environmental consultant’s investigation.”

It went on to say it takes environmental responsibility seriously.

Sutton Council told the BBC it was only notified of the breaches this month – some 16 months after Viridor first found the issue.

On Friday, council leader Barry Lewis wrote to the company and the Environment Secretary who represents neighbouring Streatham and Croydon North, raising concerns about the health impacts and reiterating its opposition to the proposed expansion of the site.

In his letter to Mr Reed, Mr Lewis said the news is “still deeply troubling” for residents.

“What is also concerning is the lack of proper monitoring and scrutiny by the EA. it is important that our residents have confidence in the ability of government regulators. This report only contributes to the erosion of that trust,” he wrote.

The government has yet to respond.

Nitrogen dioxide has been associated with adverse health effects including increased respiratory symptoms.

The UK Health Security Agency assessed local monitors following the revelation, and confirmed that daily air quality limits were not breached and “the emissions are unlikely to have caused harm to human health or the environment.”

But it also said “an exposed population is likely to be subject to potential harm at any level.”