The riskiest time in Insulate Britain’s road block protests is before the police arrive, their activists say. When they targeted a busy junction of the A1090 in Thurrock, Essex, on Wednesday morning, just outside the eastern edge of London, the police didn’t appear for nearly an hour. No serious injuries were reported, but it was close.

The first lorry, hurtling towards the T-junction, did not look like it was going to stop: it ground to a halt inches from the faces of three activists. Cars and vans mounted kerbs and central reservations to evade them. Motorists emerged from their vehicles, pink with rage, snatched protesters’ banners and dragged them from the road like ragdolls.

“Am I stopping you from insulating Britain?” one lorry driver berated them. “No, I’m fucking not. Go to the millionaire oligarchs, who own the fucking shit, and tell them to put the price down.”

In five weeks of disruptive road protests in and around London, Insulate Britain has polarised the country. Ministers have waxed apoplectic at “eco-warriors” who are “destroying people’s lives”, and Boris Johnson has called for new powers to “insulate them snugly in prison”.

But campaigners’ key demand, that the government “gets on with the job of insulating Britain’s homes” by 2030, is on everyone’s lips. Even Keir Starmer vowed at the Labour party’s conference to make home insulation a “national mission”. It is a huge impact for a group that claims at most only 120 active members.

Now, with the climate activist group announcing a 10-day pause to the campaign, ostensibly to give the government time to consider its demands, the question is what it will do next. And with the crucial Cop26 climate summit due to begin in Glasgow at the end of the month, chances are it will be something dramatic.

The night before Thurrock, 18 Insulate Britain members assembled in a rented house in south-east London. They were all in late middle age, inconspicuously dressed and well spoken – far from the “crusties” evoked in the prime minister’s denunciations. For one reason or another, they were all in a position to dedicate themselves to the cause full time.

“It’s a bit of a privilege thing,” said Louise Lancaster, 56, who quit her job as a teacher to join the campaign. “There’s obviously people in our society that there is no way they can do this, because they have to put food on the table and they can’t take time out of work. We have people of all ages, but they are quite often slightly older people or slightly younger people.”

Those the Guardian spoke to had all been involved in Extinction Rebellion, but some felt it had lost its way. “I’ve been on all these XR things; I’d go out every day and get arrested,” Chris Parish, 69, from Tower Hamlets said. “But it’s sort of somehow at the moment been subsumed by the system … It’s like a carnival. I don’t want to criticise it, but I feel like something more needs to be done.”

What sets Insulate Britain activists apart is not necessarily their willingness to go to prison, but their determination to do so. The group had hoped to have 50 climate prisoners jailed by the start of the Cop summit. “It would look so embarrassing for Boris Johnson to have elderly vicars in jail,” Lancaster said.

The group says 124 people have been arrested 629 times in 13 actions, according to its own estimates. But so far none have been held on remand for longer than a week. Police have said it is “very difficult” to bring charges against them, while the government has responded with injunctions banning them from protesting on the M25, around the port of Dover and on critical London roads.

In the kitchen, some helped prepare a meal of pasta and sauce, with rice, hummus and chopped peppers. Others gathered around the dining table, where they studied hand-drawn maps and computer printouts.

“One of the key elements in non-violent direct action is the need to disrupt,” said one activist, who preferred not to be named. “What we are really trying to do is bring economic pressure to the government through disruption, so an element in the choice of the site is trying to maximise economic disruption.”

They planned to hit a junction close to an area of warehouses and industrial units, including Amazon and Co-op distribution centres and the Daily Mail printworks. From there, lorries would be leaving to join the M25, London’s orbital motorway, to deliver goods all over the capital and south-east England.

Efforts were made to avoid critical sites such as hospitals and schools, said another activist, who also asked to remain anonymous. “Then we go to the sites to check them out,” she said. “Today there was another site I thought we could use, but there was a lot of children coming out of school and I didn’t want them to be caught up.”

Activists said that as far as they knew – and they had made inquiries, they said – no ambulances or genuine medical emergencies had been “seriously delayed” by their protests. “If we notice or hear the sirens for an ambulance, there are people who are generally moving about, coordinating and watching,” one said. Sketching arrows in pink highlighter on a hand-drawn map, she showed the route an ambulance could take through the blockade they had planned.

The following morning, looking for all intents and purposes like a church rambling group, activists travelled to Purfleet station via a chain of public transport connections. The last leg they made on the No 44 bus, arriving at about 8.30am at a desolate-looking junction by an industrial estate and an Ibis hotel.

The eyes of Jackie Doyle-Price, the area’s Conservative MP, peered across the road from a large poster. The horizon was dominated by the rise of the Dartford Crossing, a huge suspension bridge over the Thames, on which motored a steady flow of slow-moving traffic.

Assembling in a circle, they took a few final instructions. “Remember: trust in each other, trust in yourself,” said one. They waited for a gap in the traffic and walked out into the road.