The Metropolitan police’s advisers on disability have accused the force of “degrading and humiliating” treatment of disabled activists during the Extinction Rebellion (XR) protests in London this month.

A formal complaint by the Met’s disability independent advisory group says members are “disappointed and angered” the force failed to engage with them over the policing of the protests, and the Met may have caused “irreparable damage” to relations with disabled people.

Anne Novis, who chairs the DIAG, said it was the first formal complaint issued by the Met’s disability advisers in more than 20 years working as “critical friends” of the force. “We were on the point of resigning because we were hearing so many bad stories from people,” she said.

There were a series of confrontations between disabled activists and police during XR’s “autumn uprising” protests. A number of disabled people taking part in the protests say they believe they were deliberately and aggressively targeted by police.

In one incident, police arrested a carer who came to help a seriously ill woman in a wheelchair adjust her oxygen tank as she protested outside New Scotland Yard.

Nicki Myers, an organiser of the XR Disabled Rebels group, said: “After about an hour, I needed a carer to come and adjust my supplemental oxygen and get some medication that was in the bag on the back of my wheelchair.

“[Another wheelchair user] came down to do that for me and as soon as they arrived, we became an illegal assembly under section 14 and were arrested.”

Myers and other disabled people had been demonstrating to demand the return of independent living equipment confiscated by the Met during the initial stages of the XR protests.

Equipment confiscated by police included wheelchairs, disability ramps, noise-cancelling headphones, specially adapted toilets and other items intended to make protest sites accessible to disabled people, according to sources within XR.

In its letter to the Met, the DIAG said: “The actions of the MPS [Metropolitan police service] have not been received well by the disabled and deaf community, many of whom now fear that their legal right to participate in peaceful protests can no longer be exercised if their mobility equipment is to be confiscated, and personal assistants/carers arrested.

“The effect on the relationship between the MPS and members of our community is at risk of irreparable damage. The actions in the last few weeks will have long-lasting consequences for our community and will take many years to heal.”

Novis said she had heard “horror stories” from disabled people taking part in the demonstrations, some of whom she thought may have cases against police for discrimination or violation of human rights. In one case, she said, a blind protester was released without his cane and left to make his own way home.

Martin Marston-Paterson, an XR legal support and a member of the Rainbow Rebels group, said information collected by the legal team suggested police were targeting disabled protesters as a “deliberate intimidation tactic”.

He added: “In the legal team, we were prepared for violence and collating reports of police violence. What we had not anticipated was that most of those reports would be against disabled protesters, and that is a definite pattern we have determined coming through.”

When Marston-Paterson, who has cerebral palsy and arthritis, was arrested in Trafalgar Square, he says he was the only one out of 10 kept handcuffed for the journey to the police station and police confiscated his walking stick.

“At the police station, the officer justified it on the grounds that he thought it might have been a weapon,” he said. “It looks like a medical cane, it’s not decorative or aesthetic, it’s just a metal cane.”

In response, the Met said it “does not single out or disproportionately target any group or community. If those involved in an assembly to protest break the law, they are liable to arrest.”

• This article was amended on 30 October 2019. Martin Marston-Peterson is a legal support, not a legal observer. Legal observers are supposed to be independent and not affiliated with protests, while legal support is part of XR.