The letter - backed by Nestle, IKEA, Brunel, Aviva Investors, E.ON, and many other CEOs, including the bosses of a host of trade bodies and campaign groups - warned that diluting policies designed to accelerate the rate of home insulation, roll out green heating technologies and enable the transition to electric vehicles would undermine British competitiveness.
'100% committed': Sunak vows hit to net zero targets as he scraps key climate policies
"The business community has already made substantial investments in the net zero transition and made it clear that sticking to long-term net zero policies is crucial to build business confidence and mobilise investment," the letter stated. "Watering down these policies would damage the UK's credibility as a good place for green investment, undermining British competitiveness. We are already losing investment to the US and EU, and rowing back would make it worse."
The group also flagged a recent analysis from the Office for Budget Responsibility, which highlighted "the economic benefits of rapid action on net zero, and the increased fiscal and debt risks associated with delay".
"Smart policies to boost clean technologies like electric vehicles and efficient, low carbon heating and more support for the most vulnerable will lower the cost of living. Sticking with petrol cars and gas boilers increases it," the letter stated. "Slowing down the development of clean tech leaves households exposed to volatile fossil fuel markets for longer and puts jobs at risk. It is also costly for the public purse, which spent £40bn last winter subsidising household energy bills.
"We urge you not to weaken any net zero policies. If you do so, we believe this would be a historic mistake of your premiership, which could do lasting damage to the UK economy. It would also undermine the UK's international climate leadership at a time when the disastrous effects of climate change are impacting the UK and rest of the world, including the recent flooding in Libya and forest fires in Greece. Now is not the time to delay in the face of the greatest threat facing the world. Now is the time for action."
The letter was sent ahead of the prime minister's speech and press conference late yesterday afternoon (20 September), which was hastily rescheduled after Number 10's plans to water down a series of climate policies were leaked to the BBC.
In the speech, Sunak confirmed the government would delay the date for ending the sale of new internal combustion engine petrol and diesel cars from 2030 to 2035, delay and weaken a series of targets for phasing out gas boilers, and axe planned energy efficiency standards for households. He also ruled out a series of green behaviour change policies and recycling reforms that had been proposed by campaigners, but which the government had never adopted.
Sunak argued the controversial changes were needed to ensure households did not face excessive costs from the switch to EVs, heat pumps and more building energy efficiency upgrades. But he also insisted the UK would meet all its emissions targets, including both near term targets for the 2030s and the overarching goal to achieve net zero emissions by 2050.
'Investors spooked': Rishi Sunak confirms speech on the future of UK's net zero plans
The prime minister's insistence the new plans were compatible with the UK's emissions targets was dealt an immediate blow when the Climate Change Committee issued a statement confirming that it thought the reforms were "likely to take the UK further away from being able to meet its legal commitments".
Piers Forster, chair of the CCC, said: "The government not only has a legal obligation to meet its net zero 2050 target. It also has a commitment to hit the interim emission reduction targets it has put into law.
"The Climate Change Committee has an obligation to assess progress towards those targets. In June, we said in our progress report that we were less confident in the government's ability to deliver its 2030 and 2035 commitments than we were a year previously.
"We need to go away and do the calculations, but today's announcement is likely to take the UK further away from being able to meet its legal commitments. This, coupled with the recent unsuccessful offshore wind auction, gives us concern."
In his press conference, Sunak insisted he was "100% committed" to meeting all the UK's emissions targets, including those for 2030, and argued accelerating adoption of EVs and other clean technologies meant ministers were confident the targets would be met. He also announced plans to increase grants for heat pump installations to £7,500, introduce a new £150m green research and skills programme, and push through reforms to accelerate grid connections for clean energy projects.
But Forster argued that "more action is needed".
"We await the government's new plan for meeting the targets and look forward to receiving their response to our progress report, expected at the end of October," he added.
The CCC's response will be seized upon by environmental campaigners, who are already pursuing legal action against the government, alleging its current Net Zero strategy is already insufficiently ambitious and detailed to ensure legal emissions targets are met.
Emma Pinchbeck, chief executive of Energy UK, warned that surprise policy changes risked undermining investment.
"Sudden changes to policies and targets like this are damaging to the very investment we need to fund the move towards net zero and jeopardise the economic benefits and opportunities this transformation could bring in terms of jobs, growth and greater prosperity to all parts of the country," she said. "Businesses need certainty and stability when making long-term investments worth billions of pounds and targets help provide exactly that. That way businesses can invest, innovate and bring down the costs of low-carbon technologies that we need to adopt like heat pumps and electric vehicles - exactly as they have been doing.
"As recently as yesterday, ministers were stressing their continuing commitment to these policies - so it is alarming for companies considering UK investments in these areas when these same policies are shelved the next day."
Climate Change Committee warns UK has 'lost' its global net zero leadership position
Pinchbeck also questioned the prime minister's assertion that net zero policies would drive up costs for households.
"The prime minister also talked about the cost to households but it cannot be emphasised enough that what has hit people in the pocket hard over the last 18 months - through record energy bills, the resulting effect on inflation and the cost-of-living - has been the cost of oil and gas," she said. "By slowing efforts to reduce our dependency, we do leave our economy and our people at the mercy of volatile expensive fossil fuels for longer."
The government also faced international criticism at the UN's Climate Ambition Summit in New York, with former US Vice President Al Gore labelling the moves a "shocking and disappointing" decision.
"I have heard from many of my friends in the UK, including a lot of Conservative party members who have used the phrase ‘utter disgust'," Gore told CNN. "And some of the young people there feel as if their generation has been stabbed in the back. It is really shocking to me."