The government had been due to rule next week on whether planning permission for the pit near Whitehaven should be granted or not.
But, amid major climate concerns, ministers have now said they will make a decision by 8 November instead – when a new prime minister will be in place.
The proposed £165m facility, which would be the first new coal mine opened in the UK in 30 years, has been at the centre of debate since plans for it were first unveiled in 2018.
Supporters, which initially included the local county council, say it would bring vast employment and infrastructure opportunities in one of the country’s poorest regions.
But opponents have called the idea an environmental catastrophe. It would, said Lord Deben, chair of the Climate Change Committee, be an act that was “absolutely indefensible”.
Announcing the delay in a letter to interested parties, Greg Clark, secretary of state for levelling up, housing and communities, said: “This is a complex matter and officials are not yet in a position to complete their considerations prior to providing advice to ministers.
“In these circumstances, given the imminent decision date, an additional period of time is required. Planning ministers will therefore not be in a position to reach a decision on this application by the previously notified date.”
It is the third deadline that has been set after a planning inquiry was held in September last year – which itself was only launched after the government U-turned on an initial refusal to hold a review of Cumbria County Council’s decision to approve the mine.
The original deadline had been 7 July, the day prime minister Boris Johnson resigned throwing the government into disarray.
Reacting to the news of the new delay, Victoria Marsom, from Friends of the Earth, said: “The case against this coal mine is overwhelming regardless of how many times the decision is delayed…
“Fossil fuels cause enormous damage to both our environment and economy. Areas like Cumbria should be at the heart of building the greener future we need, so they can reap the benefits of the new jobs and opportunities this would bring.”
But Mike Starkie, elected mayor of Copeland, which includes Whitehaven, said he was “absolutely furious” at the new delay.
He said: “This is a planning decision we shouldn’t have to wait for a Prime Minister to be elected. The planning inspector has made his recommendation and I’m going to write to the Government and say the very least they can do is make the planning report public.”