Carole Cadwalladr’s High Court victory against Brexit donor Arron Banks shows more must be done to protect journalists from “expensive and onerous legal battles”, press freedom campaigners say.

Businessman Banks had sued investigative journalist Cadwalladr over comments she made during a TED talk in April 2019.

In a decision handed down on Monday, Mrs Justice Steyn found Banks was correct that the TED talk had caused ‘serious harm’ to his reputation, but said Cadwalladr’s claims were made in the public interest, which is a legal defence against defamation proceedings. Banks tweeted on Monday that he would “likely appeal” the decision.

Advocates say the law must be changed to “weed out abusive cases at an early stage” to avoid a chilling effect on public interest journalism. Even as the eventual winner in the case, Cadwalladr had to fundraise her way through her three-year court battle.

Cadwalladr – who won awards for her coverage of the Cambridge Analytica scandal regarding the illicit harvesting of personal data for targeted political advertising – said she was “so profoundly grateful and relieved”.

She added: “Thank you to the judge, my stellar legal team and the 29,000 people who contributed to my legal defence fund. I literally couldn’t have done it without you.”

Free speech campaign group Index on Censorship said the victory could not be called an “outright win for media freedom”.

“No journalist should be forced to spend years tied up in expensive and onerous legal battles to defend their public interest work,” it said. “Public interest journalism is the lifeblood of our democracy.”

The organisation said new measures were needed “including legislation that can weed out abusive cases at an early stage. We need journalists to be able to hold power to account for the good of our media freedom and our democracy.”

The National Union of Journalists called Banks’s defamation case an example of ‘strategic lawsuit against public participation’ (SLAPP) – legal action taken against journalists and whistleblowers to silence them – although Mrs Justice Steyn held it was “neither fair nor apt” to describe it as so.

In response to Monday’s judgment, National Union of Journalists general secretary Michelle Stanistreet said: “This is the right result, and the NUJ and all journalists will welcome the judgement and feel relieved that Carole has won this case. However, she should never have been put in the position of having to go through such a long and arduous ordeal.

“No journalist should be targeted and subjected to legal action in this way. This type of lawfare is cynical and targeted, pursued by those with deep pockets in a manner intended to pile as much pressure on an individual freelance as possible. Carole’s journalistic career has been dedicated to investigative reporting that is squarely in the public interest. Legal practices that are designed to stymie and thwart journalistic investigations and reporting need to be closed down.

“As part of our work campaigning against SLAPPs, the NUJ is calling for a series of measures to ensure that investigative reporting in the public interest is protected from those that seek to undermine journalists and journalism.”

Rebecca Vincent, director of operations and campaigns at international non-profit campaign group Reporters Without Borders, said: “We are thrilled that the High Court has issued this landmark ruling in favour of press freedom. Today is a victory for Carole Cadwalladr, whose courageous investigative journalism and fight back against this abusive lawsuit will have important implications for press freedom, but also journalism as a whole. We are proud to have stood by her side in this crucial fight.”

Concerns have been growing about the use of the courts to silence journalists. A recent Foreign Policy Centre report highlighted the use of SLAPP lawsuits against journalists.

Last year, openDemocracy revealed that it had been subject to legal threats from Democratic Unionist Party leader Jeffrey Donaldson. The case was never brought to court.

In March, the High Court dismissed a libel claim brought by an international mining company against journalist Tom Burgis.