Tesco is facing an unlimited fine after it admitted in court that it was responsible for a leak of thousands of litres of fuel that polluted a 10-mile stretch of river in Lancashire.

Petrol from the supermarket’s Haslingden filling station leaked underground into Langwood Brook, a tributary to the River Irwell, in July 2014.

Tesco Stores Limited pleaded guilty to contravening the requirements of an environmental permit and contravening health and safety regulations at Burnley Crown Court on Monday.

The company will be sentenced at Preston Crown Court in January, at a hearing that is expected to last three days. The maximum sentence it faces is unlimited fines and compensation.

Prosecuting, Richard Bradley said he would be relying on the evidence of an expert in the use and storage of dangerous chemicals.

Defending, Mark Harris said his client had acted quickly and efficiently and pleaded guilty when the case came to court.

After the case a Tesco spokesman said: “It would not be appropriate to comment on an ongoing inquiry.”

The prosecutions were brought by the Environment Agency and Lancashire County Council after 23,500 litres of petrol escaped from the filling station between 2 and 3 July 2014.