Correspondent Martha Fairlie has the main take-aways from Tuesday's hearing
It's been a three-and-a-half years since Ms Rooney accused Ms Vardy or someone with access to her personal Instagram account - of leaking stories about her private life to the media.
In a now-viral social media post in October 2019, Ms Rooney said she had carried out a “sting operation” in an attempt to find out who had been leaking "false stories" from her private Instagram account.
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The stories included Ms Rooney travelling to Mexico for a “gender selection” procedure, her planning to return to TV, and the basement flooding at her home.
In a now infamous post on Twitter and Instagram, Ms Rooney wrote: “I have saved and screenshotted all the original stories which clearly show just one person has viewed them.
“It’s………. Rebekah Vardy’s account.”
Ms Rooney, the wife of former England star Wayne Rooney, earned the nickname "Wagatha Christie" thanks to her social media probe.
Ms Vardy, 40, who is married to Leicester City striker Jamie Vardy, denies the accusations and is suing Ms Rooney for libel. Under English defamation law, Ms Rooney must prove her post was “substantially true”.
So after just one day in the High Court, what have we learnt so far and what are the standout moments?
Ms Vardy “was sometimes irritated” by Ms Rooney
Disclosed WhatsApp messages between Ms Vardy and her agent Caroline Watt showed that "in private Ms Vardy often uses strong language”.
“What those exchanges show was that Ms Vardy was sometimes irritated by Ms Rooney, rightly or wrongly,” Ms Vardy's barrister Hugh Tomlinson QC said.
“She said rude things about her, she used four-letter words.
“It’s not unknown for people to talk in private conversation in ways that they wouldn’t talk about in public.”
"Only two real suspects" in the case
The court heard from Mr Tomlinson that Ms Vardy’s agent, Ms Watt had recently withdrawn a witness statement from the trial in which she said she had not leaked stories.
Ms Watt also withdrew a waiver that might have allowed Sun journalists to say whether or not she was the source.
Ms Rooney's barrister, David Sherborne, claimed there were “only two real suspects” over the leaking of Ms Rooney’s private information, Ms Vardy and Ms Watt.
He said there were some “hopeless, speculative theories” that a hacker was involved, but the barrister dismissed these as “wild speculation” with no evidence to support them.
He said there were, in text message exchanges between Ms Vardy and Ms Watt, examples of the pair discussing leaking other people’s private information.
This included one exchange, he told the court, in which Ms Vardy said “I just don’t want it coming back on me”. He said Ms Watt replied “I can tell someone” and Ms Vardy answered by saying “yeah, do it”.
Did Ms Vardy try to move seats at a 2018 World Cup match to be more prominent in paparazzi photos?
Ms Rooney’s barrister Mr Sherborne asked Ms Justice Steyn for permission to introduce a witness statement from Harpreet Robertson, who was family liaison officer for the Football Association during the Euro 2016 and World Cup 2018 international football tournaments.
Mr Sherborne said the statement was “responsive” to evidence in Ms Vardy’s statement that at the Euros in 2016, where she first got to know Ms Rooney, her friends sat behind Ms Rooney because they were the “nearest seats available”.
The barrister said in court documents: “In fact, Ms Robinson explains that this is untrue.
“Ms Robinson recalls the seats reserved for (Ms Vardy) were seats 20-25 of the fifth row, while (Ms Rooney) was correctly sat in seats 1-6 of the eighth row.
“The seats behind (Ms Rooney) were reserved for Ms Robinson and security, and when she asked them to move the guests refused, in abusive terms.”
Ms Robertson’s statement also “addresses the fallout from (Ms Vardy’s) orchestration of the photograph outside the restaurant in St Petersburg during the 2018 World Cup”.
Rebekah Vardy regrets her Peter Andre 'expose'
Ms Rooney’s barrister Mr Sherborne asked Ms Vardy questions about an interview she gave to the News Of The World about her claimed sexual encounter with singer Peter Andre.
Mr Sherborne showed what appeared to an A3 print out of the article to Mrs Vardy in the witness box before reading the headline which spoke about the size of Mr Andre's genitals.
The barrister read excerpts from the article, in which it was claimed Mr Andre had “the smallest trouser equipment" Ms Vardy had "ever seen”.
Mr Sherborne suggested to Ms Vardy that the News Of The World was the “highest-circulating newspaper at the time”, read by some four million people.
She said: “I was forced into a situation by my ex-husband to do this. It is something that I deeply regret… It is not nice to read and I understand why this is being used and to me this is mudslinging and I was also threatened with mudslinging by Ms Rooney’s team.”
Rebekah Vardy “has no personal knowledge” of an incident where her agent’s phone fell into the North Sea
The court previously heard that Ms Watt’s phone fell into the North Sea after a boat she was on hit a wave before further information could be extracted from it in August 2021.
Ms Vardy’s barrister Mr Tomlinson said in his written arguments: “Ms Vardy has no personal knowledge as to this incident. All she knows is what has been said by Ms Watt.
“It has not been suggested that Ms Vardy had any involvement with this and it cannot possibly be relied on as evidence of wrongdoing by Ms Vardy.”
The trial continues on Wednesday.