Boris Johnson is set to announce steeper cuts to the Britain's carbon emissions.
The Prime Minister will commit to slashing emissions by 78% by 2035 compared with 1990 levels, according to the Financial Times.
The pledge is expected as the UK prepares to host the COP26 international climate change summit in Glasgow in November.
It would mark a significant step forward on the current UK commitment to cut emissions by 68% by 2030 – already one of the most ambitious plans among developed nations.
Emissions from international aviation and shipping are likely to be included, it is reported, making the target even harder to meet.
The announcement is expected before a major US summit on Thursday where President Joe Biden is expected to set out a new US target for reducing emissions.
The new target, if confirmed, would be in line with the recommendations of the Climate Change Committee, published last year, for the Government's sixth carbon budget.
The Business Department said ministers would make an announcement "shortly".
A spokeswoman said: "We will set our ambition for carbon budget six shortly, taking into account the latest advice from the Climate Change Committee."
Such a high target would mean dramatic changes to how Brits live their lives, including travel and heating their homes.
But Shadow Business Secretary Ed Miliband accused the Government of repeatedly failing to match words with action.
"While any strengthening of our targets is the right thing to do, the Government can't be trusted to match rhetoric with reality," he said.
"We need a government that treats the climate emergency as the emergency it is.
"This year, as hosts of COP26, the UK has a particular responsibility to lead the world and show the way forward for a greener future.”