St Andrews University graduate, Emma Smart, 44, said that she believes her intentions are “morally right” even if her actions are deemed “legally wrong”.
Nine supporters of the group, including Ms Smart, were jailed at the High Court in London after they admitted breaching an injunction by taking part in a blockade at junction 25 of the motorway during the morning rush hour on October 8.
Some of the group glued themselves to each other and two glued themselves to the road, causing disruption for over an hour and a half on the busy motorway.
Ana Heyatawin, 58, and Louis McKechnie, 20, were jailed for three months, while Ms Smart, Ben Buse, 36, Roman Paluch-Machnik, 28, Oliver Rock, 41, Tim Speers, 36, and James Thomas, 47, received four-month sentences.
Ben Taylor, 37, was given a longer sentence of six months “to deter (him) from committing further breaches” after his submissions to the court on Tuesday were described by Dame Victoria Sharp as “inflammatory” and a “call to arms”.
Ms Smart announced her intention to go on hunger strike immediately and said in a statement, released after she and the other activists were taken to the cells by security officers, that the Government is “betraying us”.
She said: “Our Government is betraying us, betraying our vulnerable people and betraying our children’s future.
“I believe that my intentions are morally right, even if my actions are deemed legally wrong.
“This court may see me as being on the wrong side of the law, but in my heart I know I am on the right side of history. I will not be a bystander.”
Duncan Smith, executive director of operations at National Highways, said: “Safety is our top priority and we welcome this outcome.
“We respect people’s right to protest but do not condone the actions of anyone who puts their lives, and the lives of road users, at risk.
“The judge’s decision will hopefully make people think again about carrying out reckless and dangerous protests such as these and endangering people’s lives.
“The injunctions remain in place and we stand ready to do what is necessary to limit the impact of any protests on the strategic road network, and to keep drivers safe and on the move.”
Dame Victoria, 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 the protest was “bound to give rise to frustration and anger”, which in turn endangered the public, protesters and police officers tasked with removing them from the road.
The judge added: “In a democratic society which recognises the right to freedom of peaceful assembly, protests causing some degree of inconvenience are to be expected and, up to a point, tolerated.
“But the words ‘up to a point’ are important. Ordinary members of the public have rights too, including the right to use the highways.
“The public’s toleration of peaceful protest depends on an understanding that, in a society subject to the rule of law, the balance between the protesters’ right to protest and the right of members of the public to use the highways is to be determined not by the say-so of the protesters, but according to the law.”
The judge also said the public has an “interest in deterring disobedience to its orders and in upholding the rule of law”.
The group and their supporters chanted “We are unstoppable, another world is possible”, as they were led to the cells through the dock by security officers.
After the ruling, a number of Insulate Britain activists gathered outside the Royal Courts of Justice, where one of the group read a statement from the jailed protesters, referred to as the Highway Nine.
Police watched as the group, many wearing orange hi-visibility vests, gave speeches, chanted, sang songs and held large banners.
The statement read: “To the public, we say: no-one is coming to save you.
“In the past, when governments have failed to protect their people, the right thing to do is to highlight this injustice, breaking the law if needed. This is what the suffragettes and Martin Luther King did, and it is what Insulate Britain has done.
“We call on you to recognise that you also have a duty to act, as our Government is betraying us.
“They can’t even act to insulate Britain. What hope do we have of them protecting our children, our economy or our country?”
Insulate Britain says it intends to continue the protests, which have sparked anger among motorists and others affected by the blockades, until the Government agrees to insulate homes.
Myriam Stacey QC, representing National Highways, told the court on Tuesday that the injunction banning protest activity on the M25 was granted by a High Court judge on September 21.
The High Court has so far issued five injunctions to prevent protesters from blocking roads.
They include four granted to National Highways, banning demonstrations on the M25, around the Port of Dover and on major roads around London, and one to Transport for London (TfL).
TfL was granted a civil banning order aimed at preventing protesters from obstructing traffic on some of the capital’s busiest roads.
Those who breach the injunctions could be found in contempt of court and face a maximum penalty of two years in prison or an unlimited fine.
Ms Stacey said the legal costs of the proceedings against the nine were £91,000 and asked the court to order them to pay as this was from public funds.
She argued that, even if they are unable to pay, such an order would be an “important symbol”.
Dame Victoria said she and Mr Justice Chamberlain will give their decision on costs in writing at a later date.