The miner’s Q1 data released Friday marked 1.4 million tonnes of coal produced on the quarter compared to 2.1Mt a year earlier.

The company said the slump was mostly due to technical complications at its Daw Mill operation which is the largest coal mine in the UK.

The statement comes as local media reported the coal miner is threatening to close Daw Mill because of an impasse with workers’ unions over pay and shift patterns.

“It has reached a critical point. The company can’t afford to keep running Daw Mill as it is,” the company was quoted as saying in UK newspaper The Guardian in March.

“The mine is at risk but the company will not be put at risk by a single pit … This company is not in good shape.

“We are ring-fencing each mine and Daw Mill has been the poorest performer.”

Net debt for the company was $US247.6 million at the end of the first quarter excluding restricted cash balances.

UK Coal is the largest coal producer in the UK and supplies the country with 5% of its energy needs through underground and surface mining.

The company’s first quarter 1.4Mt production total equates to 1Mt of coal from underground mines and 0.4Mt from surface mines.