The last date to buy a new petrol, diesel or hybrid car in the UK will be brought forward from 2040 to 2035, under government plans.
The change is being made to help Britain achieve virtually zero carbon emissions by the middle of the century.
The policy will be unveiled at an event to launch Glasgow's hosting of a United Nations climate summit in November.
But it could be overshadowed by a blast from the summit's former head, who was recently sacked by the prime minister. In a bitter retaliatory letter, Claire O’Neill accused Boris Johnson of promising money and people to support her work, but failing to deliver either.
The former Conservative government minister said: “The cabinet sub-committee on climate that you promised to chair, and which I was to attend, has not met once.
“In the absence of your promised leadership… departments have fought internal Whitehall battles over who is responsible and accountable for (the conference)”.
Downing Street has not yet replied to her accusations but Mr Johnson will hope that the letter will be trumped by the appearance of Sir David Attenborough at the launch event for COP26.
The prime minister will say the government plans will bring an end to the sale of new petrol and diesel cars even earlier than 2035, if possible.
Hybrid vehicles are also now being included in the proposals, which were originally announced in July 2017. The change, which will be subject to a consultation, is being planned because experts warned the previous target date of 2040 would still leave old conventional cars on the roads after the clean-up date of 2050.
COP26 is this year's meeting of the annual UN-led gathering set up to assess progress on tackling climate change Mr Johnson is expected to say: “Hosting COP26 is an important opportunity for the UK and nations across the globe to step up in the fight against climate change.
“As we set out our plans to hit our ambitious 2050 net zero target across this year, so we shall urge others to join us in pledging net zero emissions.
“There can be no greater responsibility than protecting our planet, and no mission that a Global Britain is prouder to serve.
“It will be the year when we choose a cleaner, greener future for all.”
Mrs O’Neill differs. She says at this stage, the UK should have clear actions to communicate to the diplomatic network, an agreed plan of ministerial international engagements led by the prime minister, and a roadmap for the Year of Action.
“As of last Friday, we did not,” she regrets.
One source close to Mrs O’Neill said: “Boris doesn’t really know anything about climate change. He pays lip service, but hasn't got a clue.”
Mrs O'Neill herself has warned: “We are almost out of time to win the battle against climate change and start the process of climate recovery.”
“It became clear to me that the current format of the global talks needed to be re-energised and focused.
"The annual UN talks are dogged by endless rows over agendas, ongoing unresolved splits over who should pay and insufficient attention and funding for adaptation (to inevitable climate changes).
"It was particularly awful at the last conference in Madrid. While half a million climate action protestors gathered in the streets, I sat in plenary sessions where global negotiators debated whether our meeting should be classified as “Informal” or “Informal-Informal.
“There is,” she said, “ a yawning gap between what the world expects from us and where we are. It’s a systemic failure of global vision and leadership.”
Mrs O’Neill recommends: Setting Net Zero emissions as the target for all climate ambition from countries, businesses, states and citiesIntroducing a “properly-funded” global package for adapting to inevitable changes in the climatePlacing nature-based solutions (such as forest conservation) at the heart of the agendaA new net zero sector deals from hard-to-decarbonise sectors such as cement and chemicals.
Her comments are not just aimed at government.
She criticised some climate negotiators, too, for refusing to accept that the annual parade of climate conferences won’t deliver the cuts needed for a stable climate.
“For some it is hard to give up on incrementalism even when it is demonstrably failing," she said.
“In my judgement, this isn’t a pretty place for us to be to be and we owe the world a lot better.”
Her words are likely to resonate round the world, although she is not the first climate diplomat to express this sort of frustration and she is unlikely to be the last.
Commenting on plans for a ban on sales of new petrol and diesel vehicles, Friends of the Earth’s Mike Childs said: “The government is right to accelerate the phase-out of petrol and diesel cars to curb air pollution and address the climate emergency, but the ban should start in 2030 – not 2035.
“A new 2035 target will still leave the UK in the slow-lane of the electric car revolution and meantime allow more greenhouse gases to spew into the atmosphere"
“If the UK government wants to show real leadership ahead of this year’s climate summit it must also urgently reverse its plans for more climate-wrecking roads and runways – and pull the plug on its support for new gas, coal and oil developments.”
AA president Edmund King said: “Drivers support measures to clean up air quality and reduce CO2 emissions but these stretched targets are incredibly challenging.
"We must question whether we will have a sufficient supply of a full cross section of zero emissions vehicles in less than 15 years."