A proposed new coal mine in Cumbria has been branded "absolutely indefensible" by the chairman of the government's official advisors on climate change.
Lord Deben, chair of the Climate Change Committee (CCC), was speaking at the launch of the annual report on the UK's progress in tackling greenhouse gases.
A decision on planning permission for the mine near Whitehaven to source coal for steel-making is expected soon.
Environmentalists have warned that demand for coking coal is declining.
Lord Deben, who leads the independent advisory committee, said Russia's invasion of Ukraine meant the government should be looking to protect energy supplies.
He acknowledged that the UK had done so with a focus on renewables and nuclear.
"As far as the coal mine in Cumbria is concerned, let's be absolutely clear, it is absolutely indefensible," he said.
"First of all, 80% of what it produces will be exported, so it is not something largely for internal consumption.
"It is not going to contribute anything to our domestic needs in the terms we're talking about, the cost of energy and the rest."
He said the mine's backers claimed it would provide metallurgical coal, which is currently imported, but it would not reduce the amount of coal being produced - largely in the USA.
During Prime Minister's Questions on 22 June, Boris Johnson appeared to hint that the mine may be given the go-ahead when he said that "plainly it makes no sense to be importing coal, particularly for metallurgical purposes, when we have our own domestic resources."
The mine was approved by Cumbria County Council in October 2020, but the decision was suspended weeks later following guidance from the CCC and then the Planning Inspectorate was tasked with examining the arguments.
Its report was handed to the government earlier this year and a deadline of 7 July was set for a decision by the Communities Secretary Michael Gove.
However, Lord Deben warned its approval would damage the UK's leadership on climate change and "create another example of Britain saying one thing and doing another".
He said the government should find a way of ensuring the jobs that might have been created by the mine be replaced by alternative green jobs.
Lord Deben said he was not concerned about keeping a coal-fired power plant open longer than planned this winter to shore up energy supplies, despite a commitment to end UK coal power by October 2024.
"We are under serious threat because of the invasion of Ukraine by the Russians, and in those circumstances the government has to make sure that we keep the lights on," he added.
Friends of the Earth energy campaigner Tony Bosworth said Lord Deben was "right" and the case against a new coal mine was "overwhelming in climate terms".
He said the "market for its coal is declining before it even opens", adding: "Saying no to this mine should an open-and-shut case for a government serious about the climate crisis."