British Prime Minister Boris Johnson will commit to cut carbon emissions by 78% by 2035, almost 15 years earlier than previously planned, in one of the most ambitious environmental targets set out by a developed nation.

Johnson will make the commitment this week ahead of a U.S. climate summit that will be hosted by President Joe Biden and before Britain hosts the United Nations Climate Change Conference, known as COP26, in November, a person familiar with the situation said.

The Financial Times said emissions from international aviation and shipping were likely to be included in the target.

"We will set our ambition for Carbon Budget 6 shortly, taking into account the latest advice from the Climate Change Committee," a spokeswoman for the business department said.

Britain's education secretary Gavin Williamson told Sky News that Johnson had always been clear that the country would be a global leader in cutting emissions.

"We were the first country to enshrine in law our commitment to getting to net zero," he said. "We recognise there are significant challenges with that and there's going to be significant investment."

Britain set a net zero greenhouse gas emission target in 2019, in line with the 2015 Paris climate agreement which called on countries to take steps to keep the global temperature rise as close to 1.5 degrees Celsius as possible.

The opposition Labour Party and environmental campaign groups welcomed the ambition, but said the move was undermined by a lack of policies to deliver it.

Ed Miliband, Labour's business spokesman, said the government needed to match "rhetoric with reality" and provide decisive action.

Caroline Lucas, parliament's only lawmaker from the Green Party, said the government now needed to cancel road building plans and leave fossil fuels in the ground.

(Reporting by Kate Holton and Elizabeth Piper in London; Additional reporting by Derek Francis in Bengaluru; Editing by Kim Coghill and Philippa Fletcher) ((derek.francis@thomsonreuters.com; +91-9986311363 and @derekfrancis089 on Twitter;))