The new Conservative government must urgently bring forward plans to fulfil its pledge to cut greenhouse gas emissions to net zero by 2050 or risk losing the fight against climate breakdown, green campaigners have urged.

Rebecca Newsom, the head of politics at Greenpeace UK, said the Tory manifesto was “full of holes” on the environment and had been judged inadequate by green groups, and people would expect swift action.

“The weight of responsibility and growing public concern now rests on Boris Johnson’s shoulders to ensure the UK rises to the challenge, fights for climate justice and shows real leadership,” she said.

“The next five years are make or break for the climate and nature emergencies, so we expect the new government to immediately roll out bold commitments to tackle the challenge. This should start with a climate emergency budget to pledge at least 5% government spending per year to deliver a fairer and greener economy for all.”

Climate breakdown was one of the top concerns of younger voters during the election campaign, and Labour made it the centrepiece of its “green industrial revolution” pledge to voters.

Environmental issues did not figure highly in the Tory manifesto, and Boris Johnson refused to attend a televised debate on the climate crisis, but the party remains committed to the 2050 target set as one of the last acts of Theresa May’s administration.

In a Brexit-dominated election, climate concerns appear not to have been decisive in the crucial battlegrounds of the north of England and the Midlands.

The Green party enjoyed an unexpected surge, with about 850,000 votes across the country compared with 300,000 in 2017, though it was still left with only one MP, Caroline Lucas, who increased her majority in Brighton Pavilion.

In some key marginals, Green voters made a clear difference to the result. Theresa Villiers, the environment secretary, held on to her Chipping Barnet seat against a Labour challenge by a margin smaller than the number of votes cast for the Green party candidate.

Siân Berry, one of the Greens’ co-leaders, said: “The Green party piled on votes because this was a climate election – we set the agenda and we won the argument on massive investment in a green new deal. If Boris Johnson wants to unlock Britain’s potential, he must flood every region of this country with investment to kickstart a renewables revolution, retrofit millions of homes and build up decent local transport. We haven’t got five more years to waste.”

Nick Molho, the chief executive of the Aldersgate Group of green companies, said businesses were eager for the government to quickly come up with detailed plans for the environment. “Businesses want the government to hit the ground running in 2020, with urgent policy decisions needed on the environmental and climate agenda,” he said.

“Key priorities should include putting together credible plans to deliver and fund the net zero transition, and introducing an ambitious environment bill to safeguard the proper enforcement of environmental law and introduce legally binding environmental improvement targets.”

Among the few green pledges in the Tory manifesto was a promise to spend more than £9bn on insulating and retrofitting homes and buildings to high environmental standards, and to encourage take-up of electric vehicles.

Analysis before the election found that the record of the last three Tory and Tory-led governments since 2010 was patchy, with reversals on key policies such as renewable energy, support for electric cars and insulation.

For international observers at the final day of the UN climate talks in Madrid, Johnson’s landslide victory cleared the way for the UK’s presidency of the COP26 talks scheduled for next November in Glasgow.

There, the world will decide on the future of the Paris agreement and countries will be expected to come up with strengthened targets on cutting greenhouse gas emissions in line with scientific warnings.

As host, the UK government will play a key role in the success or failure of the talks, and experts said behind-the-scenes diplomacy must begin in earnest now.

“We saw in Paris that the degree of success depends very much on the presidency [of the host nation],” Nat Keohane, a senior vice-president at the US-based Environmental Defense Fund, told the Guardian. “The UK needs to being doing a full-court press on diplomacy right now to make this a success.”

Tom Burke, the chair of the UK-based E3G environmental group, said: “Having just reaffirmed Britain’s commitment to climate change, the prime minister is now going to have to make a global success of COP26, and that will make for an interesting conversation with President Trump [who is withdrawing the US from the Paris agreement].

“This means he will need to put a minister with real political weight in charge of the preparations. Given the size of his majority, he will have no excuses if his government fails to deliver on its environmental promises.”