Malcolm Turnbull has announced that, from now, sexual relations between ministers and their staff will be prohibited under a change he has made to the ministerial code of conduct.

Addressing a news conference late on Thursday, Turnbull also strongly hinted he would like to see Barnaby Joyce step down.

Joyce had made “a shocking error of judgement in having an affair with a young woman working in his office”. In doing so he had set off a “world of woe” for his wife, daughters and indeed his new partner, and had “appalled all of us”.

When asked why he wouldn’t urge Joyce to resign, Turnbull pointed out that he was leader of the minor party in the Coalition.

But his preference was clear. “Barnaby has acknowledged his fault, his error, his grief about his conduct. He has to consider his own position obviously. These are matters for Barnaby Joyce to reflect on.”

Earlier Turnbull told parliament that when he visits the US next week, Senate leader Mathias Cormann – not Joyce – would be acting prime minister.

Turnbull said the ban on sexual relationships would apply even if the minister was single.

The ban parallels a prohibition last week passed by the US House of Representatives – although that was included in legislation while this is only in the ministerial code, and is only enforceable politically not legally.

It also follows a call by crossbencher Cathy McGowan last week for a “conversation” about conduct between MPs and their staff. Her call was dismissed at the time.

Turnbull said then: “Members of parliament, ministers all have to be accountable for their actions. As grown-ups, we are all accountable for our actions. Relations between consenting adults is not something that normally, you would be justified in, if you like, seeking to regulate.”

But government sources said Turnbull had been working on the sex ban all week.

Turnbull told his news conference the Joyce affair had raised “some very serious issues about the culture of this place, of this parliament”.

He said the present ministerial code was “truly deficient”.

“It does not speak strongly enough for the values that we should all live, values of respect, respectful workplaces – of workplaces where women are respected.”

He said this respect in workplaces was not entirely a gender issue. But “most of the ministers, most of the bosses in this building” were men and “there is a real gender perspective here”.

He said that whatever people might have turned a blind eye to in years past, in 2018 it was not acceptable for a minister to have a sexual relationship with someone who worked for them.

“It’s a very bad workplace practice. And everybody knows that no good comes of it.

"Of course you know what attitudes in the corporate world and elsewhere are to this kind of thing. So, it is about time that this change was made. Probably should have been made a long time ago.”

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.