A libel row between Countdown co-presenter Rachel Riley and a political blogger over an article that alleged she engaged in a “campaign of online abuse and harassment” against a teenager has reached the High Court.

Riley is suing Michael Sivier, who published an article on his website Vox Political on January 26 2019 with the headline “Serial abuser Rachel Riley to receive ‘extra protection’ – on grounds that she is receiving abuse”.

The article discussed tweets posted as part of an online debate on antisemitism in the Labour Party, some of which were exchanged between Riley and a user, who identified herself as a then-16-year-old called Rose, in December 2018 and January 2019.

A judge previously found that Mr Sivier’s article would be read as claiming Ms Riley “engaged upon, supported and encouraged a campaign of online abuse and harassment of a 16-year-old girl”, allegations denied by Riley.

The blogger is defending the claim by arguing he had a “reasonable belief” it was in the public interest to publish the claims in the article.

At the High Court in London on Monday, Riley said the amount of abuse she received increased significantly from January 9 2019.

She said: “That’s when the floodgates opened. I changed my Twitter settings after that week because it was so horrendous.”

She continued: “It was a whole load of abuse that I was receiving, that Channel 4 was receiving.”

David Mitchell, for Mr Sivier, later accused Riley of having double standards.

He said: “When it comes to your political opponents… You can accuse them of antisemitism or anything you see fit, but those standards don’t apply to you or anyone who you see as your political allies.”

Riley said the claim was “nonsense”, adding: “When someone is not antisemitic, it is not double standards to say it is not antisemitic.”

Mr Mitchell also argued that Riley had not provided any evidence to show she had faced serious harm connected to the article.

The barrister said in written submissions: “The claimant has a reputation for being highly controversial and offensive.

“It is denied that the defendant’s publication could have caused or had the tendency to cause serious harm to this reputation.”

However, John Stables, for Riley, said the allegations Mr Sivier published caused Ms Riley serious harm.

“Given the gravity of the allegations made against the claimant and the extent of their publication, the objectively determinable harm caused by the defendant’s publication is so great as easily to surmount the threshold of serious harm,” he said in written submissions.

Mr Sivier had originally defended the libel claim on the grounds of truth and honest opinion as well as public interest.

In January 2021, Mrs Justice Collins Rice struck out all three of Mr Sivier’s defences, finding that they had “no prospect” of succeeding at a full trial.

However, Mr Sivier won a challenge at the Court of Appeal four months later, finding that his public interest defence should be assessed at a trial.

The trial before Mrs Justice Steyn is due to finish later this week, with a decision expected at a later date.