A PONY was found up to its belly in thick mud after a Hillingdon firm polluted a stream between Harefield and Ruislip.

Dirty water escaped from a site operated by Arbormaster (UK) Ltd three years ago when staff washed soil. The muck travelled into fields and a stream called Mad Bess Brook.

The pony broke free from the sludge, but Arbormaster, of St Leonard’s Farm, New Year’s Green Lane, Harefield, was fined £3,500 for the incident and failing to obtain a permit from the Environment Agency for the work.

In February 2016, the Agency was asked to investigate reports from people that the River Pinn, some distance from the Arbormaster plant, had become cloudy at several locations downstream of Ruislip.

Officers were unable to prove the muddy water had travelled eight kilometres to the Pinn, but they traced the pollution back to Mad Bess Brook and St Leonard’s Farm.

They found a large quantity of murky water cascading down the side of a pile of waste soil. The water drained away from the farm via a ditch connected to the stream.

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The discoloured liquid was discovered shortly after Arbormaster had installed a machine at St Leonard’s Farm to clean waste soil used in landscaping.

The Environment Agency ordered the company to stop the process because of the pollution.

District Judge Deborah Wright, sitting at Ealing Court last week, called the company’s actions reckless.

James Burton, a senior environment officer, said: “Pumping large amounts of water into a waste pile without any way of capturing the liquid was inevitably going to cause a problem.

“The Environment Agency can work with companies to make sure they comply with the law, but enforcement is always open to us.”

Arbormaster pleaded guilty to two breaches of environmental law.

In addition to the fine, the court ordered it to pay costs of £5,000 and a victim surcharge of £170.