"I'd like to say that it's absolutely important,it's incredibly important that there be a circuit-breaker,not just for the Parliament,but more importantly,a circuit-breaker for Vikki,for my unborn child,my daughters and for Nat. This has got to stop. It's not fair on them."

Mr Joyce,who was first elected to Senate in 2004,said he would not quit the Parliament but,rather,would head to the backbench and continue work on a book and promised"no,I won't snipe". Considered one of the nation's best"retail politicians",he switched from the Senate to the House of Representatives in 2013,and became leader of the Nationals in 2016,the same year he became Deputy Prime Minister.

Last year he was forced to quit Parliament and contest a byelection after he was found to be a dual New Zealand citizen and therefore constitutionally ineligible for election.

A move to the backbench would mean he would give up the portfolios of Infrastructure and Transport and his salary would drop from $416,000 to about $200,000 a year. The new National Party leader would become deputy prime ministerunder the Coalition agreement.

The decision to quit comes less than 24 hours after backbench Nationals MP Andrew Broadcalled on him to quit,and two days after Mr Joyce and Ms Campion grantedan exclusive interview to Fairfax Media in which the pair appealed to politicians and members of the public to"move on"from the scandal.

That interview had the opposite effect to that intended,stoking anger within the Nationals that the former deputy prime minister - who was supposed to be on a week of personal leave - was instead kicking the story along.

Mr Joyce said he had finally decided to quit following the airing of allegations of sexual harassment in a Sydney tabloid,which he said he had only become aware of"in the last day or so".

"Over the last half a month,there has been a litany,litany of allegations. I don't believe any of them have been sustained,"he said.

"The last allegation that was in the paper today,I have asked that that be referred to the police. I've asked for the right of the person who's made the allegation and I've asked for my right of defence that that be referred to the police. But it's quite evident that you can't go to the Despatch Box with issues like that surrounding you."

"I can't enter into any discussions about that. If it is going to be before the courts,it is going to be before the courts."

Soon after the announcement the Prime Minister's office issued a statement thanking Mr Joyce for his service as a"fierce advocate for rural and regional Australia".

"The Coalition between the Liberals and the Nationals is Australia’s most successful political partnership,having endured for more than 95 years,"it said.

"This partnership is undiminished and will continue to deliver opportunity and security for all Australians."

Mr Joyce put himself on a collision-course with Mr Turnbull last Friday,when he launched an extraordinary attack on the Prime Minister,calling his comments on the affair"inept","unnecessary"and"hurtful".