The Metropolitan Police has said it will appeal against a High Court ruling that it breached the rights of organisers of a vigil for Sarah Everard.
The founders of Reclaim These Streets (RTS) had brought a legal challenge against the force over its handling of the event planned to be held near where the murdered 33-year-old went missing in Clapham, south London, last March.
They withdrew from organising the vigil after being told by the force they would face fines of £10,000 each and the threat of prosecution if it went ahead, given coronavirus-related curbs in place at the time.
A spontaneous assembly and protest took place instead and the police were criticised for their actions after women were handcuffed and led away by officers.
In a ruling earlier this month, two senior judges found the Met's decisions in the run-up to the planned event were "not in accordance with the law".
Scotland Yard has said it had "taken time to consider" the ruling and wants to "resolve what's required by law when policing protests and events".
But London mayor Sadiq Khan has said he was "extremely concerned" about the decision to appeal and would raise it with outgoing Met commissioner Dame Cressida Dick.
"The abduction and murder of Sarah Everard by a serving police officer has massively damaged the confidence of Londoners, particularly women and girls, in the police," a spokesman for Mr Khan said.
"In the wake of such a horrendous crime, the policing of the vigil in her memory eroded trust even further," he added.
A statement from the Met said: "It's absolutely right that we are held to account for our actions and that there is proper scrutiny of the decisions we make as a police force in upholding legislation and maintaining public order.
"We also respect the strong views held by Reclaim These Streets in defence of human rights and public protest, and their pursuit of justice for these views.
"As an organisation, we work with, support and police hundreds of protests and events across London every day and take our responsibilities under the Human Rights Act in doing so very seriously.
"It's important for policing and the public that we have absolute clarity of what's expected of us in law.
"This is why we feel we must seek permission to appeal the judgment in order to resolve what's required by law when policing protests and events in the future."
RTS co-founder Jamie Klingler was among those to express anger at the announcement and accused the force of wanting to "exhaust us".
"I'm not going to pretend I am not furious," she tweeted.
Activist Patsy Stevenson, who was pictured being detained at the vigil in a photograph widely shared, tweeted: "Still can't hold themselves accountable."
Ms Klingler along with Jessica Leigh, Anna Birley and Henna Shah had argued that decisions made by the force in advance of the planned vigil amounted to a breach of their human rights to freedom of speech and assembly, and said the force did not assess the potential risk to public health.
Upholding their claim, the High Court found the Met had "failed to perform its legal duty" to consider whether the women might have a reasonable excuse for holding the gathering.
Ms Everard was murdered by serving Met officer Wayne Couzens, 49, who was given a whole life sentence at the Old Bailey in September.
This week Couzens was charged with four counts of indecent exposure which allegedly took place in the weeks before he killed Sarah Everard.