The government’s pledge to reach “net zero” carbon emissions by 2050 is not drastic enough, according to environmental campaigners.

The UK is set to become the first major economy to commit to completely avoiding emissions from homes, transport, farming and industry or offsetting them by planting trees and sucking carbon dioxide (CO2) out of the atmosphere.

The amendment to the Climate Change Act has been widely welcomed as a significant milestone.

However, some environmental groups are concerned that even this pledge does not go far enough and they have raised concerns about the UK using international carbon credits to shift the burden of carbon cutting to other nations.

Craig Bennett, UK chief executive of Friends of the Earth, warned it was “still too slow to address catastrophic climate change”.

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He said the next prime minister must put carbon-cutting “at the centre of policy-making and pull the plug on plans for more roads, runways and fracking”.

Legislating for international carbon credits means the UK could pay for other countries to cut their carbon instead of reducing domestic emissions. Critics said this showed the government is not taking the issue seriously enough and could mean it shirks environmental obligations.

“It is disappointing that the government has ignored its climate advisers’ recommendation to exclude carbon offsets," Mr Bennett said.

He added: "Having declared a climate emergency, parliament must act to close these loopholes.”

Doug Parr, Greenpeace UK’s chief scientist, also said it was a “big moment” for the climate, but added there were “questions to be asked about (the) offsetting loophole”, which has a history of failure.

“As the birthplace of the industrial revolution, it is right that the UK is the world’s first major economy to commit to completely end its contribution to climate change, but trying to shift the burden to developing nations through International Carbon Credits undermines that commitment,” he said.

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Professor Mark Maslin, professor of climatology at University College London (UCL), said Britain should adopt a 2030 zero carbon target. He said that if there was any chance of keeping the planet from warming more than 2C, the whole world must hit zero carbon emissions by 2050.

“Britain is one of the leading countries in the fight against climate change and we must adopt a 2030 zero carbon target," he said. "This will give us 10 years to put in place win-win solutions that reduce carbon emissions, save money and make Britain a better, cleaner place to live."

Climate change activists Extinction Rebellion, who staged demonstrations in a number of British cities earlier this year, blocking parts of central London for days, were most scathing about the 2050 target, describing it as a “death sentence”.

Number 10 said the move would boost public health, air quality and nature and will make the UK a leader on climate action. But it said it was “imperative” other countries follow suit.

The government will review the pledge within five years to ensure other nations are taking similarly ambitious action and that British industries are not facing unfair competition.

Lord Deben, chairman of the government’s advisory Committee on Climate Change, praised the “major commitment” and said he was looking forward to cross-party consensus on the issue.

“This step will send a strong signal to other countries to follow suit – and will help to drive the global effort to tackle climate change required by the Paris Agreement,” he said.

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Dame Carolyn Fairbairn, director-general of business group the Confederation of British Industry (CBI), said UK companies were “squarely behind” the commitment and called it the “right response to the global climate crisis”.

But she urged the government to ensure the legislation was followed by long-term policies to support decarbonisation across the economy.

Hitting net zero – a 100 per cent cut in emissions – will mean an end to heating of homes with traditional gas boilers, more green electricity, and a switch from petrol and diesel cars to electric vehicles, walking and cycling.

Any remaining pollution in 2050 from areas including aviation will need to be “offset” through measures to cut carbon such as planting trees.

Environment analyst Tom Burke said there was “quite a gap” emerging between announcements on climate change and the implementation of policies.

“The reality is it’s what you do, not what you say, that matters," he told BBC Breakfast. “There’s been quite a gap, in a way, emerging recently between what the government has said it wants to do on climate change and the fact that the policies aren’t in place to deliver on the existing budgets, let alone the carbon budgets we’ll need if we’re to meet this new commitment.”

Shadow energy secretary Rebecca Long Bailey raised concerns over how the commitment would be put into practice.

“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.