Oil refiner Ineos has written down the value of its Grangemouth, UK petrochemical plant to zero, it said, further raising the stakes in a complex dispute with workers at the facility who are due to start industrial action this week.

The privately owned, Swiss-based refining and chemical plant owner Ineos said it had invested more than £1 billion since taking over at the Grangemouth plant in 2006, but that it continued to lose money.

"We had no option but to write down these assets," Calum MacLean, chairman of the Grangemouth Petrochemicals Business, said in a statement. "After four years of heavy losses, the petrochemicals business is effectively worthless. Without lower costs and an alternative source of additional raw material it will close 2017, at the latest."

Writing down the value of the plant could put pressure on the workers to accept lesser terms and conditions in their dispute with Ineos.

The Grangemouth petrochemical plant in Scotland is attached to a 210,000 barrel per day refinery, which Ineos jointly owns with PetroChina.

Oil traders are closely watching the dispute, as the refinery provides steam for a pipeline that brings crude oil from the Forties North Sea oilfield, one of the four crude grades that underpins the Brent benchmark.