Insulate Britain has declared the M25 a “site of non-violent civil resistance” and called for motorists to keep to 20mph on the motorway or avoid it altogether, after a new injunction banned the group from major roads across England.

It comes after Grant Shapps, the transport secretary, announced that England’s roads agency, National Highways, had obtained an injunction banning the group from protesting across England’s “entire strategic road network”.

A 251-page annexe to the injunction, published on the National Highways website, specifies every road from which the group is banned.

The activists’ response to the injunction came on a day when a brief but testy exchange between one of its spokespeople and the TalkRadio presenter Mike Graham went viral after the latter suggested that concrete could be grown like trees.

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Speaking to the Guardian after the interview, the spokesperson, Cameron Ford, 31, from Cambridge, said: “If these people are responsible for informing the public what a 2C [of global warming] world looks like, when they don’t even know what can and can’t grow on this planet, then we are in trouble.”

Insulate Britain said its M25 declaration was a response to the latest injunction, the fifth taken out against the group. It has repeatedly defied previous orders, placing members at risk of prosecution for contempt of court, which can lead to a two-year jail sentence and an unlimited fine.

The group said in a statement: “Starting from 7:00 on the morning of Wednesday 27th October the M25 will become a place of nonviolent civil resistance to stop our government committing crimes against humanity.”

Insulate Britain resumed its campaign of disruptive protests on roads in and around London on Monday morning after a 10-day pause, with three roadblocks in the financial district.

In a statement on its website, the group said it was asking for drivers to avoid using London’s orbital motorway, or if they do to keep their speed to 20mph “to reduce the risk of accidents”. It also called on National Highways to enforce this new speed limit and on the police to refuse to arrest its members, “as we are upholding the British constitution and they have a duty to refuse to obey any government that fails to uphold its first and most important responsibility: the protection of people in Britain.” It said access would be granted to emergency vehicles.

Shapps said new legislation would give the criminal justice system the power to handle protest groups such as Insulate Britain. “The long-term solution lies in changes to the police, crime, sentencing and courts bill, giving additional powers against disruptive protests which target critical national infrastructure,” he said on Twitter. “This includes unlimited fines and prison sentences of up to six months for obstructing highways.”

Insulate Britain has staged 14 days of action on critical roads around London since 13 September, leading to hundreds of arrests. The group had originally intended to have dozens of “climate prisoners” in UK jails by the start of the Cop26 climate summit in Glasgow at the end of October, but so far none have been held for more than a week.