The school strikes movement will ensure an exciting and dynamic future for environmental activism for decades to come, the outgoing head of Friends of the Earth has said, as students across the globe leave classrooms on Friday to demand political action on the climate crisis.

Speaking on the first anniversary of the movement in the UK, Craig Bennett said it was grassroots activism, not centralised politics, that was leading to change.

“What we are seeing is a new kind of informed and exciting activism,” said Bennett. “What excites me most is seeing the awakening of communities. To see the school strikes – to see the next generation of activists coming through – could not be more exciting for the movement long term.

“To have a whole generation coming through going on these demonstrations, where is that going to take us? What is going to happen in 10 years’ time when they start being in employment? Are they suddenly going to turn off the activism? I don’t think so, and that is what is really hopeful for the environmental movement.”

Bennett is leaving the environmental charity after 18 years, the last five as head of the organisation. In that time, the group has shifted its focus from the past tactics of lobbying Westminster politicians to the creation and development of a grassroots base of activists.

In the last 18 months 150 new community action groups have been created by the movement, while supporters of the environmental charity have more than doubled from about 160,000 to more than 400,000.

The move to tap into and amplify community frustrations at the failure to do enough to tackle climate breakdown has coincided with the growth of the school strikes movement and the appearance of Extinction Rebellion.

“We have got to use the politics on the ground rather than rely on centralised institutions and politicians to do it for us,” he said.

Bennett – who will take over as head of the Wildlife Trust in April – believes the explosion of activism has been caused partly by the deep frustration of ordinary people that we are not making fast enough progress to tackle climate change, combined with growing evidence from scientists that the world has an ever decreasing amount of time to make change.

“There is something that is unique about these issues,” said Bennett. “The longer we take to achieve the change, the worse the prize of the outcome. It is quite different to, say, campaigning for the abolition of slavery … the prize you get is still the same, even if it takes 100 years to get there.

“But campaigning for eight or nine billion people to live fairly within environmental limits, the longer you take to do it, the lower the quality of the prize you get.”

In his tenure at Friends of the Earth, Bennett has focused on community-based action against fracking in the UK, activism that was rewarded last year when the government announced a moratorium on fracking.

He believes it is community activism that has pushed the government to act against fracking, and prompted the attention Boris Johnson’s government is giving to environmental concerns. Last week Johnson brought forward the deadline for ending the sale of diesel, petrol and hybrid vehicles from 2040 to 2035.

“It is primarily because of people on the streets that this is happening,” said Bennett. He pointed to polling by the thinktank Bright Blue showing that climate change and the environment were crucial to gain the support of the centre ground in British politics. “People care about the environment more than ever before,” said Bennett.

Faced with what he believes are small moves by the government, Bennett says the environmental movement, including the school strikers, must continue to demonstrate and push for more rapid change. The government’s target of reaching net-zero carbon emissions by 2050 was important, but lacked any detail, he said. The prospect of the UK hosting the UN climate summit in September without “the first clue” of how to reach net zero as a nation was “unbelievably embarrassing”, said Bennett.

“There is no plan to get to there,” he said. “The committee on climate change has produced a report on how to get there, but that is not government policy.

“Where is the plan to cut UK carbon emissions by somewhere between 50% and 80% by 2030? That is what we need, at the very least. We need to be cutting emissions by about 15% each year from today. What matters is less the talk about net zero, but how fast we can cut emissions within the lifetime of this current parliament.

“Given Boris Johnson has a stonking majority, he has no excuse and this government should do exactly what is required.”