The fusty confines of London’s high court get the Hollywood treatment this week when it considers a blockbuster libel action and hears evidence from major movie stars.

Johnny Depp’s claim against the Sun over allegations that he was violent towards his ex-wife, Amber Heard, 34 – allegations he vehemently denies – has been more than two years in gestation.

But it could see him demoted from the Hollywood A-list overnight.

The 57-year-old actor is suing the Sun’s publisher, News Group Newspapers (NGN), and its executive editor, Dan Wootton, over a 2018 article which referred to the star as a “wife beater”. In an article under the headline: “Gone Potty – How can JK Rowling be ‘genuinely happy’ casting wife beater Johnny Depp in the new Fantastic Beasts film?” Wootton questioned why the author was content for the actor to appear in the latest movie to be hewn from the Harry Potter franchise.

That the case – which was due to start in March, but was delayed because of the Covid-19 pandemic – has made it to the high court is unusual. Most libel cases get settled for pragmatic reasons.

“The costs that each side will incur tend to be pretty significant,” explained Emily Cox, partner in the media disputes division at law firm Stewarts, who suggested both parties could “quite easily” end up spending £1m each fighting their corner.

She added: “Loser pays winner’s costs in this jurisdiction but you don’t tend to recover all of your costs. The reasonable best case is you would get 70% of your costs back.”

Cox said it was hard to see any damages awarded to Depp, if his claim were successful, to exceed the £185,000 the BBC paid Lord McAlpine after a Newsnight broadcast led to him being wrongly implicated in child abuse. But Depp, who intends to travel from his home in France to London to give evidence, may have felt he had no choice but to take action. The allegations threaten to curtail a coruscating career.

“He’s not going to want to remain on the record as somebody who committed domestic violence,” Cox said. “In a #MeToo world there’s much less tolerance of that kind of allegation.”

Tactically, the Sun trial is the first battle in a longer war. Depp is suing Heard in the US for $50m in damages over a column she wrote in the Washington Post in which she described herself as a “domestic abuse” victim. Although Depp was not named in the column, he claims it defamed him.

In legal documents filed by Heard in response, the Aquaman star claimed Depp regularly beat her up before she married him in 2015 and that this continued during their 18-month marriage. Depp, who denies the claims, has in turn accused Heard of attacking him. The UK case therefore may have an important bearing on the US action. “If he gets a strongly worded judgment in this jurisdiction that will go a huge way to clearing his name,” Cox said.

With reputations at stake, legal skirmishes fought before the case has even been heard suggest armies of skeletons will be dragged from cupboards. NGN’s lawyers accused Depp of being in “serious” breach of a court order because he had failed to provide key texts between him and an assistant. The lawyers said the messages, sent in Australia in February and early March 2015 – shortly before what Heard claims was “a three-day ordeal of physical assaults” – demonstrated that Depp was trying to obtain drugs.

The alleged incident in Australia is one of 14 separate allegations of domestic violence that NGN intends to rely on in its defence.

Mr Justice Nicol refused an application from Depp’s lawyers for Heard to disclose evidence including an audio recording of a conversation between herself and her former husband. The lawyers had also asked for “all communications” between Heard and a contact saved in her phone as “Rocketman”, whom Depp claims is Tesla and SpaceX founder Elon Musk, and between Heard and actor James Franco.

But rejecting the application, Nicol said: “The central issue for the defence of truth is whether Mr Depp assaulted Ms Heard.”

Depp will reportedly call ex-partners including Vanessa Paradis and Winona Ryder as witnesses to vouch that he was never violent towards them.

Both Depp and Heard – who is believed to have already travelled to the UK from California – are expected to spend two or three days being questioned in the witness box. Fighting on Depp’s side is an attorney and lobbyist, Adam Waldman, who was instrumental in the star’s recent decisions to sue his former lawyer and management agency.

One source who knows Waldman told the Observer that he was “a pitbull” who was “very well connected”. Waldman is known to have lobbied for the oligarch Oleg Deripaska, and visited WikiLeaks founder Julian Assange nine times at the Ecuadorian embassy in London in 2017.

“He’s the puppet master in all this,” the source said. “He’s very litigious and very tough.”

Last week Waldman took to Twitter to berate Hollywood reporters digging into his relationship with Depp. He also published Nicol’s ruling that the trial was to proceed 40 minutes before it was released officially.

On his Twitter feed, Waldman posts claims made about his client that are later disproven or fail to materialise under the words “in memoriam”. Expect the two words to feature heavily in Waldman’s Twitter feed if Depp wins.

But if he loses, they may provide an epitaph.