Costs in the Government's legal fight over its air pollution plans have exceeded £300,000.
Environment Minister Therese Coffey revealed new figures showing the Department for Environment, Food & Rural Affairs (Defra) is estimated to have so far spent £310,000 defending its position.
She added that the bill to taxpayers is likely to rise as the case is ongoing.
Ministers were ordered to draw up new clean air plans, including how to reduce nitrogen dioxide levels in the UK, following a court challenge by environmental lawyers ClientEarth.
A further High Court challenge has followed, taking place on Wednesday, which argues that the draft measures need improving.
Labour MP Jim Cunningham (Coventry South), in a written parliamentary question, asked Environment Secretary Michael Gove "what estimate his department has made of the court costs for the air quality compliance cases brought by ClientEarth, and if he will make a statement".
Ms Coffey replied: "Defra estimates that the legal fees incurred by the Government to defend the litigation brought by ClientEarth are around £310,000.
"The case is ongoing and so further costs are likely to be incurred."
The Government is consulting on its draft measures, which include a "targeted" scrappage scheme to get older, more polluting vehicles off the roads.
Air pollution in the UK is said to be linked to an estimated 40,000 early deaths a year.