David Southwick divulged details of the surreptitious recording to the Federal Court on Wednesday in Moira Deeming's defamation trial against Victorian Opposition Leader John Pesutto.
Mrs Deeming claims Mr Pesutto defamed her by suggesting or implying she was a Nazi in comments he made following the Let Women Speak rally.
The March 2023 event was gatecrashed by neo-Nazis who performed the Nazi salute on the steps of state parliament.
Mr Pesutto has denied any wrongdoing.
Earlier in the trial, it was revealed Mr Southwick secretly recorded the meeting held between Ms Deeming and Liberal leadership the day after the rally.
In the 70-minute recording played to the court, Mrs Deeming was criticised for her involvement in the rally and for photos showing her having champagne afterwards with fellow organisers.
She is also heard telling the leaders she did not realise the Nazis were even at the rally and she did not support them.
Moira Deeming's barrister Sue Chrysanthou grilled the deputy leader about his secret recording. (James Ross/AAP PHOTOS)
Mrs Deeming's barrister Sue Chrysanthou SC grilled Mr Southwick on Wednesday morning as to why he surreptitiously created the recording.
He told the court he spoke to Mrs Deeming on the day of the rally after videos of the Nazis were circulated online and in the media.
Mr Southwick said he instructed her to issue a public statement that evening, condemning what had happened and the Nazis.
He claims she instead sent out a tweet saying she was disappointed police had walked "masked men" past the rally as they did a "horrible Nazi salute".
Mr Southwick told the court she should have been stronger in calling them Nazis and denouncing what had been "one of the darkest days" in Victoria.
David Southwick said he hoped his tape of the meeting would never have to be used. (Joel Carrett/AAP PHOTOS)
The deputy leader said he chose to record the next day's meeting because he could not trust Mrs Deeming and he needed to protect himself and the Liberal Party from what was about to happen.
"I wanted to make sure the whole events weren't turned around and misconstrued," Mr Southwick told the court.
"For me, it was an insurance policy."
The recording was uncovered a week before the trial started and Mr Southwick maintained he never intended for anyone to hear it.
The other members of the meeting did not know he was recording it on his iPhone, Mr Southwick said.
David Southwick denied withholding the tape because it contradicted John Pesutto's statements. (James Ross/AAP PHOTOS)
"I hoped that tape would never have to be used," he told the court.
"That's why I didn't talk about the tape or mention it to my colleagues."
He admitted he told Mr Pesutto about the recording in November or December last year, once it became clear the defamation case might proceed to court.
Mr Southwick denied he withheld the tape because it contradicted the statements of Mr Pesutto and other members of the Liberal leadership.
He also claimed he did not listen to the recording before making his written statement, telling the court he felt his memory was sufficient to recall what had happened.
His evidence continues.
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