More than 100 Extinction Rebellion protesters have had charges against them dropped after the ban forbidding protest in London last month was ruled unlawful.

The Crown Prosecution Service decision will affect about 105 cases immediately, mostly those involving defendants facing trial for allegedly breaching section 14 of the 1986 Public Order Act.

Others formally accused of obstructing the highway will also have the cases against them discontinued, the CPS confirmed. Many cases will still go ahead.

The announcement may encourage large numbers of the estimated 1,800 protesters who were held between 14 October and 19 October to sue for wrongful arrest and detention.

Earlier this month, the high court ruled that the section 14 order obtained by the Metropolitan police, which declared that XR “must now cease their protests within London”, exceeded the police powers.

Delivering judgment, Mr Justice Dingemans said: “Separate gatherings, separated both in time and by many miles, even if coordinated under the umbrella of one body, are not a public assembly under the meaning of section 14(1) of the 1986 act.”

As a result of that ruling, charges based on breaching section 14 orders became legally impossible to pursue. A CPS spokesperson said: “We will be discontinuing a number of cases against Extinction Rebellion protesters who were arrested during the October protests.

“These are cases in which the section 14 order was allegedly breached and some cases of highway obstruction. This decision has been taken as our legal test is not met.”

The CPS confirmed that cases involving 73 defendants charged with breach of section 14, 24 charged with breach of section 14 and highway obstruction and eight charged with standalone highway obstruction would be discontinued.

The London solicitors’ firm Hodge Jones & Allen has confirmed that many of its Extinction Rebellion clients have received confirmation that the CPS is dropping charges against them.

The firm said it was “delighted that the CPS has finally recognised the futility of their position in relation to the prosecutions of those arrested under the unlawful section 14 imposed on the protests on 14 October”. Other prosecutions relating to 8 October are also being dropped, the law firm said.

Raj Chada, the head of the protest team at Hodge Jones & Allen, said: “From the moment that the high court ruled the Met police’s ban was unlawful, this was an obvious consequence. The CPS have dithered and delayed before bowing to the inevitable and only caused more anxiety and expense to our clients.”

Extinction Rebellion said it believed charges against as many as 1,000 people would eventually be halted.

Tobias Garnett, a human rights lawyer in Extinction Rebellion’s legal strategy team, said: “Extinction Rebellion is glad to see that the Met police and the CPS have recognised the implications of our successful challenge earlier this month. It underlines the need for proper policing that doesn’t waste precious public resources.

“These admissions of unlawful arrest do not impact on other arrests for criminal damage or related to aviation and railway legislation, for example. But they do affirm that when the people of this country assemble peacefully to demand action on the climate and ecological emergency the law is on our side.”

Martin Marston-Paterson, one of those arrested under the first week’s section 14 order and a claimant in Extinction Rebellion’s Letter Before Action to the Met regarding that order’s legality, said: “I am delighted to see that the Met have conceded the illegality of the 8 October section 14 order in the light of the judgment in Jones. It is to be hoped that the police will, in future, take much greater care to act within the law and to balance the right to protest with their desire for public order.”

Jules Carey, of the London law firm Bindmans, which was instructed by Extinction Rebellion, said: “We welcome the police’s confirmation that they will not dispute the legality of their 8 October section 14 ban. While we wait for the high court to formally address the issue, it is now clear that the policing of the Extinction Rebellion protests was a mess: the right to protest was overlooked, police powers were overstepped, and a significant clean-up operation is now required in the criminal justice system to deal with hundreds of cases that should never have been brought.”