Nine Insulate Britain protesters have been jailed for breaking a court order banning them from protesting on the M25, by a judge who said no lesser penalty “would adequately mark the gravity of the defendants’ conduct”.

Ana Heyatawin, 58, and Louis McKechnie, 21, were jailed for three months while Dr Ben Buse, 36, Roman Paluch-Machnik, 28, Oliver Roc, 41, Emma Smart, 44, Tim Speers, 36, and James Thomas, 47, each received four-month sentences.

Ben Taylor was jailed for six months, with Dame Victoria Sharp, the president of the Queen’s bench division of the high court, describing his comments in court as “inflammatory” and a “call to arms”. On Tuesday he had told her he would return to block roads if she did not jail him, and promised that others would follow his example.

The judge, sitting with Mr Justice Chamberlain, said there was no alternative to custodial sentences given that the group’s actions were so serious and they had made it clear they intended to further flout court orders.

She said: “Importantly, none of the defendants has demonstrated any contrition or understanding of the seriousness of deliberately breaching a court order. Each continues to believe that his or her actions were justified.

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“The defendants, or some of them, seem to want to be martyrs for their cause and the media campaign surrounding this hearing appears designed to suggest this. We, however, have to act dispassionately and proportionately.”

Sharp said protests “causing some degree of inconvenience are to be expected and, up to a point, tolerated” in a democratic society that recognised the right to freedom of assembly.

“But the words ‘up to a point’ are important,” she said. “Ordinary members of the public have rights too, including the right to use the highways.

“By deliberately defying the M25 order, these defendants broke the social contract under which in a democratic society the public can properly be expected to tolerate peaceful protest,” the judge added, drawing a cry from Roc of “the social contract is broken”.

Myriam Stacey QC, representing National Highways, made an application to recover GBP91,000 in costs from the defendants. Owen Greenhall, representing Buse, pointed out that the sum included nearly GBP17,000 for advice alone. “That’s not a reasonable or proportionate sum,” Greenhall said.

Smart said: “I’ve spent the last three years voluntarily working in wildlife conservation and climate activism. You are claiming more for postage than I’ve earned in the last three years, which is absolutely obscene. The fact that you are profiting from our stand, trying to save the lives of 8,500 a year, I find obscene.”

As the group were led to the cells by security officers, they and their supporters chanted “we are unstoppable, another world is possible”. Outside the courtroom, supporters sang happy birthday to McKechnie, who turned 21 on Wednesday.

Insulate Britain said Smart had announced she would immediately begin a hunger strike.

Speaking to reporters outside the court, Tracey Mallaghan, a spokesperson for the group, said: “A few hundred people captured the country’s attention for months. Think what 1,000 people can achieve? You have a choice. To act, to come and join us help change the tide of history, or to be a bystander and be complicit in enabling genocide.”

National Highways welcomed the verdict. “The judge’s decision will hopefully make people think again about carrying out reckless and dangerous protests such as these,” a spokesperson said.

Raj Chada, a solicitor at the Hodge Jones and Allen law firm who supported the protesters, said: “With these prison terms, the long and honourable tradition of civil disobedience is under attack again. Rather than leaving courts to imprison those that raise the alarm, it should be the government that acts to protect us against the climate crisis.”