One of the biggest waste-management companies in the South-East has been given a record fine over illegal treatment of hazardous material including asbestos at its huge Willesden depot.

Powerday, run by London Irish rugby club co-owner Mick Crossan, disposes of waste for major clients including Barratt Homes, Berkeley Homes and Carillion.

The firm was ordered to pay more than £1.2 million at ­Harrow Crown Court for offences related to two separate cases which, ­combined, saw more than 17,000 tonnes of waste deposited and stored ­illegally. The record fine came under tough new sentencing guidelines for environmental crimes.

The first case saw Powerday storing more than 10 tonnes of hazardous waste for disposal at the Willesden site in breach of its licence.

The Environment Agency said this included asbestos, contaminated concrete and treated wood which had been taken to the Willesden centre from building sites across London and a power station in Nottinghamshire.

The company was fined for charges including “treating, keeping or disposing of controlled waste in a manner likely to cause pollution or harm to human health”.

In the second case, Powerday admitted its part in a scheme that saw approximately 3000 tonnes of contaminated material, known in the industry as “trommel fines”, trucked off from its huge Old Oak Sidings depot in Willesden to be used in compost at a mushroom farm in Oxfordshire.

The fine — part of which reflected the £350,000 extra profit Powerday made from its offences at Willesden — is thought to be the biggest of its kind.

Powerday pleaded guilty to the offences last year, but sentencing was only handed down this week.

“The Environment Agency takes tough action against illegal activity and will not hesitate to investigate and prosecute those involved in waste crime,” the agency said. “Illegal waste activity undermines nesses and puts the public and environment at risk.”

The agency was alerted to the mushroom farm dumping after receiving reports from the public of lorries apparently containing waste entering the farm’s gate.

Powerday’s managing director Mark Bensted wrote to the court along with other directors to express remorse and state they had cleaned up the contaminated land.

Owner Crossan said he was “frustrated that the case got to this point”, acknowledging there was a breach arising out of what he described as an “ambiguity” in the licence at Old Oak Siding. He added that Powerday had since introduced improved governance and management systems.