Insulate Britain campaigners blocked slip roads and the M25 carriageway itself in a number of locations and poured paint on the roads that will require cleaning, leading to further disruption, the group said.
Police were called to Junction 18 of the M25, the Amersham and Watford turnoff, and near Junction 4 of the A1M, near Hatfield, shortly after 8am on Monday morning as many demonstrators glued themselves to the road.
The blockage caused traffic to pile up across the three M25 anticlockwise lanes near Junction at 8.40am.
Photos show protesters blocking traffic by sitting on the roads as they held signs saying “Insulate Britain”.
Shortly before 9am, police were seen taking away protesters - a total of 29 arrests have been made.
Hertfordshire Constabulary Chief Superintendent Nick Caveney said: “Protesters have made it clear that they intend to continue causing disruption.
"Not only is purposely blocking a highway incredibly dangerous, it also affects thousands of members of the public who are stuck in delays as a result.
“We have robust plans in place in order to minimise any disruption and to allow us to make arrests as quickly as we possibly can. This includes, but is not limited to, monitoring areas that have been identified as possible protest targets.
“Officers were on the scene within minutes of being alerted to protest activity, allowing us to put diversions in place to ease the traffic and to make numerous arrests. All protesters involved in this morning’s protests have been arrested and will be taken to custody.
“We are working closely with other affected forces to ensure that any further activity is dealt with effectively and efficiently.
“I understand and appreciate the frustration regarding the considerable delays and inconvenience that has occurred as a result of the protests.
“We have now made a total of 76 arrests in relation to protest activity across Hertfordshire over the last week. Please be assured that a full investigation is under way, and we are in the process of gathering evidence in order to ensure that those breaking the law are brought to justice.”
A statement from Insulate Britain said: “Early this morning, Insulate Britain blocked the M25 for a fourth time.
“Actions will continue until the government makes a meaningful commitment to insulate all of Britain’s 29 million leaky homes by 2030, and all social housing by 2025.
“People blocked slip roads and the M25 carriageway itself in a number of locations. Once again, blue paint was poured onto the road, which will require cleaning, leading to further disruption.
“Many of those blocking the roads today have participated in all four actions to date.”
The group wrote to National Highways and the police to alert them to the action on Monday, so speed limits could be reduced on the major motorway.
It is the fourth time the group has blocked traffic on the M25.
On Friday morning, protesters targeted Junctions three, at Swanley in Kent, nine at Leatherhead in Surrey, and 28, near Brentwood in Essex. Surrey Police said officers had arrested 14 people at junction nine.
Last Monday, the offshoot of Extinction Rebellion staged sit down protests at Junction 3 for Swanley in Kent, Junction 6 for Godstone in Surrey, Junction 14 for Heathrow Terminal 5, Junction 20 for Kings Langley in Hertfordshire, and Junction 31 for Purfleet in Essex. A total of 78 people were arrested following the demonstrations.
Foreign Office minister James Cleverly told ITV’s Good Morning Britain the protesters are “adding nothing” to the cause of tackling climate change.
He said: “It is a completely inappropriate way of making the point they’re trying to make, and I know the police have been taking action, the home secretary has made it very, very clear that they should be taking action, the police should take action when people are taking part in criminal behaviour, and that’s what I think everybody will expect.”
He said the protests were “ego-driven”, and added: “I think the vast, vast majority of people want to see us tackling climate change, we are tackling climate change, the UK is one of the global leaders in this and this is very much what the prime minister will be taking with him as a message when he goes to the United Nations, or now that he’s at the United Nations General Assembly.
“We’ve got the fastest reduction of emissions of any major developed economy, the UK is actually a real leader on this.
“So I have to say, my belief is that those disruptions and protests are more ego-driven, rather than issues-driven. And I would strongly urge the people involved in it not to put themselves and others at harm by this continued disruption.”
“These protesters are waking up at lunchtime and claiming credit for the sunrise. The simple fact is the UK is already pushing the world to do more and we are walking the walk as well as talking the talk and these protesters are adding nothing to that discussion.”