Mark McGowan has defended his rhetoric against Clive Palmer, saying the billionaire’s “deeply offensive” statements had contributed to death threats against him and his family.

Giving evidence on Monday in the Federal Court in Sydney, the West Australian premier said various public comments by Mr Palmer had left him extremely angry and hurt, and caused him many sleepless nights.

Mr Palmer is suing Mr McGowan for defamation, claiming public comments – including labelling the Queensland businessman the “enemy of the state” – had damaged his reputation.

The premier has lodged a counter-claim that he was defamed in several of Mr Palmer’s interviews and statements.

Among these was a claim in July 2020 that he had lied by claiming to have acted on the chief health officer’s advice in implementing a hard border closure.

Mr McGowan described some people in WA as having been in a “state of terror” about the COVID-19 pandemic.

“For a national figure like Mr Palmer to accuse me of lying in that context … was a deeply offensive statement that I had to endure,” he told the court.

“I had literally people coming to my house in Rockingham yelling at my wife and children about … how we had to take action, people in a state of quite heightened anxiety in the community.

“I am actually prone to sleepless nights and at that point in time I had a lot of sleepless nights worrying about everything that was going on.”

Mr McGowan described various threats made against him and his family throughout the pandemic, including a package containing white powder being sent to his wife and a person driving an armoured car with fake machine guns to his electorate office.

He now has a police car constantly parked outside his home.

“My entire family is under threat because of all this madness that people like Mr Palmer stir up,” he said.

Mr Palmer’s barrister Peter Gray SC grilled the premier on his repeated claims that the hard border closure was necessary based on medical advice.

He referred to written advice provided in late-March 2020 by WA’s top health officials, who said closing the border would slow the spread of COVID-19 but would have a relatively small impact compared to other measures.

“The suggestion it was necessary because of health advice was a lie, wasn’t it?” Mr Gray asked.

“I disagree with that,” Mr McGowan replied.

Mr Palmer and his company Mineralogy launched a failed bid in the High Court in 2020 to have WA’s hard border declared unconstitutional.

One of Mr Palmer’s complaints relates to Mr McGowan saying the businessman “wanted to come to Western Australia to promote hydroxychloroquine to the people of the state as some sort of cure for COVID”.

Mr Palmer has previously said he thought it looked like a promising treatment for the virus.

But he insisted he wasn’t promoting anything and said the comment made him seem “equivalent to a drug dealer”.

The premier said his top health officials had recoiled at the thought of using the anti-malaria drug to treat COVID-19.

Asked about his description of Mr Palmer as the “biggest loser” – a quip referring to his physique – Mr McGowan described it as “a bit of fun” and probably a cheap shot.

Further background to the case relates to the McGowan government introducing extraordinary legislation which prevented Mr Palmer and Mineralogy from suing the state for billions of dollars over the Balmoral South iron ore project.

In his evidence last month, Mr Palmer said he was “scared” because provisions in the legislation protected the government from criminal prosecution.

Referring to the fictional character James Bond and his “licence to kill”, Mr Palmer told the court: “I didn’t know what the limits might be.”

The billionaire publicly claimed Mr McGowan had engaged in a “concerted effort to cover up his personal involvement in breaking the law”.

Mr McGowan said the suggestion he was corrupt was a deep wrong against his character.

He described Mr Palmer’s attempt to claim up to $30 billion in damages from the state as an act of “extraordinary greed”.

Mr McGowan is due to resume his evidence on Wednesday.

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