Theresa May has sought to cement some legacy in the weeks before she steps down as prime minister by enshrining in law a commitment to reach net zero carbon emissions by 2050, making Britain the first major economy to do so.

The commitment, to be made in an amendment to the Climate Change Act laid in parliament on Wednesday, would make the UK the first member of the G7 group of industrialised nations to legislate for net zero emissions, Downing Street said.

Environmental groups welcomed the goal but expressed disappointment that the plan would allow the UK to achieve it in part through international carbon credits, something Greenpeace said would “shift the burden to developing nations”.

Last week No 10 dismissed claims from the chancellor, Philip Hammond, that such a target would cost £1tn and could thus require spending cuts to public services.

With May departing as prime minister next month, as soon as her successor is chosen, she has stepped up efforts on policy areas sidelined by Brexit, including new spending commitments, efforts to tackle modern slavery and the environment.

The 2050 target, in an amendment being put down as a statutory instrument, meaning it does not require a vote of MPs, will be one of the most ambitious such goals set by a major polluting nation.

France proposed net zero emissions legislation this year, while some smaller countries have gone for dates before 2050, such as Finland (2035) and Norway (2030), though the latter allows the buying of carbon offsets.

While the 2050 date was recommended by the UK’s official Committee on Climate Change (CCC), May has rejected its advice on international carbon credits, whereby a country can pay for cuts elsewhere in lieu of domestic emissions. John Gummer, the CCC chair, said last month it was “essential” that such credits were not used.

Drax in North Yorkshire. Although it generates about 22.8m tonnes of CO2 each year, Drax is the most carbon efficient coal-fired power plant in the UK. Photograph: Jason Hawkes/Getty

Doug Parr, the chief scientist for Greenpeace UK, said the target was “a big moment for everyone in the climate movement” and a legacy May could be proud of. However, he said the “loopholes” of allowing international carbon credits would need to be unpicked and the target date moved forward.

“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. “This type of offsetting has a history of failure and is not, according to the government’s climate advisers, cost-efficient.”

May, who will mark the target on Wednesday by meeting science and engineering students, said it was “the time to go further and faster to safeguard the environment for our children”.

She said: “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. 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.”

The plan was endorsed by the CBI’s head, Carolyn Fairbairn, who said such efforts “can drive UK competitiveness and secure long-term prosperity”.

She added: “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.”

Downing Street poured scorn last week on Hammond’s warnings, disclosed in a leaked letter, saying the supposed £1tn figure ignored both the economic benefits of action and the costs of not doing anything.

A Treasury source said Hammond fully backed the 2050 net zero target but had pushed for a full costing of the plan to make sure it did not negatively impact on other areas of public spending.

May has rushed through the legislation with one eye on her legacy after being effectively forced out of office before doing everything she wanted to in terms of domestic policy.

Downing Street sources said implementing the target before she leaves No 10 in a few weeks’ time was extremely important to May. It is understood she also reminded her colleagues in cabinet on Tuesday morning that she wanted them to make sure they did not forget about dealing with the fallout from Grenfell Tower after she leaves office.