A political blogger who sparked online uproar after being arrested for filming a council hearing has been ordered to pay £25,000 in libel damages to a council's chief executive over what the high court described as an "unlawful campaign of harassment, defamation and intimidation".

Jacqui Thompson was ordered to pay the five-figure sum over a series of defamatory internet posts in which she falsely accused Carmarthenshire county council chief executive, Mark James, and other council officers of corruption.

Thompson targeted James and other council officers in letters, emails and blogposts in a five-year campaign that resulted in her arrest in June 2011, the high court ruled on Friday.

She attracted nationwide publicity after being arrested to "prevent a breach of the peace" while filming a council hearing on her mobile phone for her political blog, titled Carmarthenshire Planning Problems and More. News of her arrest quickly spread online as Twitter users posted their outrage using the hashtag #daftarrest.

Britain's most senior libel judge, Mr Justice Tugendhat, said in his ruling on Friday: "Mrs Thompson conducted her campaign of harassment as publicly as she could, at first copying her letters and emails to the press and numerous other people and, after she had started her blog, publishing her unfounded allegations to the world at large."

The judge said Thompson was motivated by revenge when she made a series of libellous allegations of corruption against council officers.

Thompson's blog was launched in 2009 and was highly critical of the council. Thompson's family had made a number of unsuccessful planning applications between 2004 and 2008, prompting her to take her complaints online.

In an 86-page judgment, Tugendhat said everyone is entitled to express opinions based on facts that are true – but Thompson had repeatedly made accusations without foundation.

He added: "Mrs Thompson's campaign of harassment and libel is the most recent of a number of cases which have recently come before the courts. Many such campaigns are not aimed at officials of public authorities, but some are.

"In Mrs Thompson's case, the motive is revenge. In other cases, the motive is financial gain, or an obsession for which there is no obvious explanation. These campaigns are commonly conducted on the internet."

Tugendhat dismissed Thompson's claim for libel against James over a letter he posted online in the aftermath of her arrest. He upheld James's counter-claim against the blogger.

In one hotly-disputed incident, Thompson falsely accused a council officer of assaulting her and attempting to steal her phone as she left the council chamber on 13 April 2011.

The judge said the defamatory internet posts about James were read by a "small number" of people – despite her blog being prominent locally and nominated in 2010 in the Media Wales "Wales Blog Awards".

In a tweet sent after the ruling, Thompson said: "just to say I am still here and I am devastated. I will make a brief statement a bit later on. #daftarrest"

Speaking after the high court hearing, Thompson told the Guardian she was "devastated" and that she did not recognise the description of herself in the judge's remarks.

"It's very damaging to me and I've just got to deal with it," she said. "I haven't got any money. I haven't got the faintest idea how I'll pay it I just really don't know how I'll pay."

She added that the judgment could have wider implications for political bloggers who believe they are writing in good faith. "For other bloggers like me they're gonna have to think twice perhaps. I hope it doesn't restrict other bloggers or cause worry but I think it might somewhere down the line," she said.

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