The climate emergency has risen to the top of the UK’s election agenda in a way that would have been “unthinkable” even five years ago, leading environmentalists have said, predicting that it augurs a permanent change in British politics.

On Wednesday, Labour took the unprecedented move of putting green issues as the top section of its manifesto, the first time one of the UK’s two major parties has done so. Jeremy Corbyn led the appeal to voters with policies including an £11bn windfall tax on oil and gas companies, a million new jobs in a “green industrial revolution” and commitments on moving to a net-zero carbon economy.

“Such focus on climate and the environment would have been almost unthinkable five years ago,” said Shaun Spiers, executive director of the Green Alliance. “Tackling climate change runs through this manifesto in a way that is unprecedented from either of the main parties ahead of a UK general election.”

“It would not have been possible five years ago,” said Tom Burke, chairman of environmental thinktank E3G and former adviser to several governments, who said the move marked a permanent change in British politics, as younger voters in particular were “energised” over the environment. Public anxiety had been fuelled by people seeing extreme weather around the world, and the rise of climate activism in movements such as Extinction Rebellion and the school climate strikes reflected that. “The politicians are following the public on this, not the other way round.”

Public concern over the climate is “unequivocal”, and people “back decarbonisation by a massive margin”, said Richard Black, director of the Energy and Climate Intelligence Unit. “The UK has never had an election like this one in terms of the profile of climate change. To have all the major parties supporting a transition to net zero within a few decades, and competing with each other on policies to deliver, is unprecedented.”

Labour disappointed many green campaigners by failing to put a date on its commitment to a net-zero carbon economy. After union pressure, a proposal to mandate the transformation by 2030 was watered down to “achieve the substantial majority of our emissions reductions by 2030”, which should imply swifter and stronger action than the Tory pledge to decarbonise by 2050, but leaves room for interpretation.

There was also no frequent-flyer levy, despite increasing concern over aviation emissions from the independent Committee on Climate Change, and a heavily hedged green light on airport expansion.

“Labour’s manifesto stops short of getting full marks – its policy for tackling exploding aviation emissions is not fit for purpose,” said John Sauven, executive director of Greenpeace UK. “And the commitments on plastic pollution and waste do not go far enough.”

Ryan Shorthouse, director of the Conservative thinktank Bright Blue, accused the party of wanting too much state control in calling for nationalisation of energy, water and railways. “[The Labour manifesto] equates to a significant and unprecedented expansion of state expenditure and control. They envisage a super-spending, suffocating state. But voters are not stupid – the state cannot and should not deliver everything.”

Burke believes Labour’s stance on Brexit will also alienate many environmentally minded voters. “Brexit is appallingly bad for the environment. The Labour party wants to do good things on the environment and wants do that within a strong EU – Corbyn is letting them down.”

However, pushing the climate emergency back to the political periphery would no longer be an option for any party, he said. “This is mainstream now.”

The Liberal Democrats, while focusing on Brexit, have also made the climate emergency a key priority, promising to generate 80% of the UK’s electricity from renewable sources by 2030, to bring forward to 2045 the deadline for net-zero carbon, and to expand electric vehicles and ban fracking. The Green party wants to spend £100bn a year for the next decade on the climate crisis, replacing high-carbon infrastructure and creating jobs.

This weekend, the Conservative manifesto is expected to include policies on combatting climate change, reconfirming its commitment to net-zero carbon. Next year, thanks to Theresa May’s offer to the UN, the UK will host the most important international summit on the climate since the 2015 Paris agreement was signed, requiring a massive diplomatic effort if the government is to make it a success. But the party may be hampered by its recent see-sawing on environmental policies, with incentives to low-carbon development withdrawn, home insulation schemes closed and incoming housing regulations scrapped.

Spiers said: “This will be a big moment for UK politics if the Conservatives show a similar level of ambition [to Labour].”