In one of her final acts as British Prime Minister, Theresa May will tomorrow move to enshrine a net zero emissions target into UK law, setting a goal to effectively end the world's first industrialised nation's contribution to global warming by 2050.

Number 10 confirmed tonight that legislation is to be laid before Parliament tomorrow morning to amend the UK's 2008 Climate Change Act and raise the current target to cut emissions by 80 per cent by 2050 to a net zero emissions goal.

The change would make the UK the first major global economy to set a net zero emissions target in law, a move the government hopes would secure the UK's position as a global leader in the fight against climate change and encourage other leading economies to follow suit.

The move follows a landmark report last month from the Committee on Climate Change (CCC), which concluded a net zero target was technically feasible, in line with the Paris Agreement, and could be achieved at a cost of around one to two per cent of GDP in 2050, before co-benefits are considered.

"This country led the world in innovation during the Industrial Revolution, and now we must lead the world to a cleaner, greener form of growth," May said in a statement announcing the decision. "Standing by is not an option. Reaching net zero by 2050 is an ambitious target, but it is crucial that we achieve it to ensure we protect our planet for future generations."

Parliament will vote on the changes in the coming days, with the new target expected to pass with a comfortable margin. MPs from across the political spectrum have called for a net zero target, the Labour opposition has backed the plan, and all of the candidates to replace May - bar one - have said they support a new target.  

The decision to boost the UK's climate ambitions comes in the wake of growing public and business pressure for more action on climate change. Britain's biggest business group, the CBI, has called for a net zero target, while polling shows climate change is now among the most pressing concerns for the British public.

CBI director-general Carolyn Fairbairn welcomed the news, declaring that "UK business stands squarely behind the government's commitment to achieve net zero emissions by 2050".

"This legislation is the right response to the global climate crisis, and firms are ready to play their part in combating it," she said. "Climate leadership can drive UK competitiveness and secure long-term prosperity."

Last month the CCC said a net zero goal for the UK was both desirable and feasible, and called on the government to set one "as soon as possible".

Pushing through the net zero legislation in her final days in office could prove to be one of May's most important, and far-reaching legacies. It will require every sector of the UK economy - including aviation and shipping, which are not officially part of existing emissions commitments - to fully decarbonise by 2050. As such, it is expected to help unleash billions of pounds in new green infrastructure investment, trigger a wave of fresh decarbonisation policies, and drive targeted R&D efforts to help tackle emissions from high carbon sectors. 

In delivering the target Downing Street looks to have faced down Treasury concerns about the cost of the net zero transition, which last week sparked fears the decision could be delayed while an additional review was undertaken.

In a leaked letter from Chancellor Philip Hammond to the Prime Minister, the Treasury warned the costs of a net zero goal could be "well in excess of a trillion pounds" and argued more research was needed to understand the potential impact on households and UK competitiveness. A number of industrial groups and unions have similarly warned that unless it is effectively managed deep decarbonisation could lead to higher costs and job losses for energy-intensive industries.

TUC General Secretary Frances O'Grady said "we now need a fair and robust plan to get [to net zero] that everyone can get behind". "That means government, business and trade unions working together on a 'just transition'," she added. "Working people must have a say through transition agreements in their workplaces. And there must be a guaranteed path to high-quality work in a green economy for anyone whose job may be at risk."

The CCC has maintained that delivering the net zero target should cost between one and two per cent of GDP by 2050, putting the net zero transition in the same cost bracket as was estimated for the original 80 per cent emissions target when the Climate Change Act passed in 2008. The Committee said rapid cost reductions for technologies such as solar and wind power meant the increase in ambition could be delivered at no extra cost to the original forecasts - an argument endorsed by Number 10.

A number of leading economists and businesses have taken issue with the Treasury's analysis, arguing the cost of inaction on climate change is far greater than the cost of decarbonising. Experts have also predicted that when co-benefits such as cleaner air and enhanced energy security are taken into account the net zero transition should deliver significant net benefits to the UK economy.

Paul Dickinson, executive chair at corporate disclosure body CDP, said "there's absolutely no question that [net zero] is the right economic choice".

"The financial cost of climate impacts is enormous while the benefits of a low-carbon economy are even greater," he added. "Just last week CDP's latest climate analysis showed that just over 200 of the world's biggest companies are exposed to close to $1tr of potential climate risks in the next five years. But it's not all bad news. They also reported business opportunities from the low-carbon transition worth $2.1tr and, crucially, estimated the value of these opportunities to be over seven times the cost of achieving them. The business case is clear, the time to act is now."

However, Number 10 has responded to some of the Treasury's concerns and tonight confirmed it will review the net zero target in five years to ensure other major economies have followed suit with "similarly ambitious action", so as to ensure UK industries "do not face unfair competition".

There are reasons to be optimistic that the UK's new target will form part of a trend. A number of countries, such as Sweden, Finland, New Zealand, and Costa Rica, have already adopted net zero targets, while the French government is currently working on similar plans and the EU is considering a target for 2050. Meanwhile, UN Secretary General Antonio Guterres has called on all governments to come forward with proposals to strengthen their domestic climate action plans before the Paris Agreement comes into full effect next year. 

Business and environmental groups hailed the new target as an historic breakthrough, but were also quick to warn that it needed to be backed by detailed new decarbonisation policies if the goal was to prove credible.

UK emissions reductions have stalled in the transport, industry, and argicultural sectors in recent years and the country is currently off-track to meet its medium term emissions targets.

"This legislation must be followed by a commitment to long-term policies that support decarbonisation across the economy," Fairbairn said. "Some sectors will need clear pathways to enable investment in low-carbon technologies, and it is vital that there is cross-government coordination on the policies and regulation needed to deliver a clean future."

The Labour opposition offered a blunter assessment, with Shadow Business Secretary Rebecca Long-Bailey accusing the government of undermining its own net zero ambitions.

"While this announcement is welcome in theory, in practice it comes from a Conservative government that is off track to meet existing climate targets, that has no plans for legislation or investment needed to cut emissions, and that has dismantled the UK renewable energy sector while pushing fracking," she said. "The government is a bit like a marathon runner with the wrong shoes, the wrong diet and no training expecting to break the world record; it looks less like ambition and more like delusion."

Putting the UK on track to meet the new target will require a rapid uptick in emissions reduction efforts across all areas of the economy. For example, the CCC advised that sale of new petrol and diesel cars would need to be banned by 2035 at the very latest, rather than the current target date of 2040; fossil fuels such as coal and gas, including shale gas, would need to be completely phased out for generating heat and electricity - unless nascent carbon capture technologies are scaled up significantly - within the next 25 to 30 years; and farming and land use would need to undergo a huge transformation to boost tree planting, enable peatland restoration, and increase the cultivation of biomass energy crops.

Lifestyle shifts are also expected to play a major part in meeting the target, with the CCC suggesting a shift to more plant-based diets would be crucial for reducing agriculture emissions, while greater use of public transport will be needed to curb pollution from transport.

But Business, Energy and Industrial Strategy Secretary Greg Clark insisted the net zero target would also unleash a wealth of low-carbon business opportunity across the UK. "We want to continue our global leadership and that's why we are introducing a legally binding net zero target to end the UK's contribution to global warming entirely by 2050," he said. "The report we commissioned from the Committee on Climate Change makes clear that we have laid the foundations to achieve a net zero emissions economy, and that it is necessary and feasible."

"Almost 400,000 people are already employed in the low-carbon sector and its supply chains across the country. Through our modern Industrial Strategy we're investing in clean growth to ensure we reap the rewards and create two million high quality jobs by 2030."

Environmental campaigners broadly welcomed the news. Greenpeace's chief scientist Doug Parr said the legislation marks a "big moment for everyone in the climate movement". But he warned the government's decision to retain its ability to use offset credits to contribute towards domestic emissions "undermines" the headline commitment. "This type of offsetting has a history of failure and is not, according the government's climate advisors, cost efficient," he said.

Parr also set out an immediate to-do list for the government to accelerate emissions reductions. "The government must immediately upgrade our electricity, construction, heating, agriculture and transport systems," he said. "It must cancel the Heathrow third runway and road-building plans, and invest public money and provide significant policy support to protect communities, workers and the planet. It's now official - in a climate emergency, business as usual is no longer an option."

Nick Mabey, CEO of climate change think tank E3G, urged political and business leaders to now seize the opportunities presented by the net zero transition. 

"As the first major economy in the world to legislate for net-zero emissions, this will inspire other countries to follow," he said. "It is an act of true leadership on the international stage. A net zero target is also critical for business, giving them the confidence to invest now in powering ahead with a prosperous zero carbon transition. But this target will be meaningless unless the government ramps up its policies and public investment to get us on track. Net Zero must now be put at the heart of the UK's economic mission and infrastructure plans."

Alongside confirmation of the new target, the government this evening also announced plans for a Youth Steering Group, which will see young people provide advice on how the net zero transition should be managed. May will tomorrow meet with young science and engineering students to discuss the new target and its implications.