Hollywood star Johnny Depp denied slapping his ex-wife Amber Heard after he became angry because she mocked him over one of his tattoos, London's High Court heard on Wednesday.

Giving evidence on the second day of his libel trial against Britain's Sun newspaper, Depp was asked by the paper's lawyer about an incident at Heard's home in March 2013 when he had "fallen off the wagon" and it was alleged he had struck her.

Sasha Wass, the Sun's lawyer, said Depp, who had started drinking again after months of sobriety, had become angry when she laughed at one of his tattoos which he had changed from "Winona forever" - a reference to his former girlfriend Winona Ryder - to "Wino forever".

He had then slapped her three times because she had initially not reacted, Wass said.

"That's not the case, that's untrue. It didn't happen," Depp said. "I don't recall any argument about any of my tattoos."

Depp is suing The Sun's publisher, News Group Newspapers, and its executive editor, Dan Wootton, over an article he wrote in which he labelled the actor a "wife beater", based on allegations from actress Heard.

The paper says its account is true and that Heard, 34, says Depp punched, slapped and kicked her during violent rages, brought on by anger and jealousy and fuelled by alcohol and drugs, which put her in fear for her life.

In evidence and in his witness statement to the court on Tuesday, Depp, 57, accused Heard, who is also attending the trial, of lying, saying she had attacked him, severing his finger off during one encounter.

He denies that he turned into "the monster" when under the influence of alcohol or drugs.

Among the evidence given to the court on Tuesday was a detailed account of Depp's heavy drinking and drug-taking, with the actor saying he had tried "every drug known to man" and spent $30,000 a month on wine.

He said he had introduced his 13-year-old daughter to marijuana, saying he wanted to be sure the drug was good quality and she was in a safe environment when she tried it, and that singer Elton John had helped him get treatment for his drinking.

Heard or her friends were also accused by Depp of defecating in their bed as a prank, and Heard was accused of having affairs with Tesla chief executive Elon Musk and actor James Franco.

The couple met on the set of the 2011 film "The Rum Diary" and married in February 2015. However, Heard filed for divorce after 15 months and their divorce was finalised in 2017. The case is set to last three weeks.