The ABC understands NSW Police will interview Nationals MP Michael Johnsen on Friday over an allegation he raped a woman in 2020.

The Upper Hunter MP strongly denies the accusation that he sexually assaulted the sex worker at a lookout in the Blue Mountains town of Yellow Rock.

He has since resigned as parliamentary secretary and will no longer sit in the Nationals party room nor joint party room while the investigation takes place.

Labor MP Trish Doyle used parliamentary privilege to raise the matter on Wednesday but did not name Mr Johnsen. He later identified himself as the accused.

Sources have told the ABC the investigation will be handed by detectives from the sex crimes squad.

Mr Johnsen said he had already spoken with police and would continue to cooperate with all inquiries.

NSW Deputy Premier John Barilaro said he asked Mr Johnsen to resign late on Wednesday.

NSW Premier Gladys Berejiklian said she was “shocked” about the allegations.

“First of all I join everyone else in being absolutely shocked at the serious allegations that were raised, and somewhat relieved that it’s subject to a police investigation.”

Ms Berejiklian said she learned of the allegations when Ms Doyle gave her explosive speech on Wednesday.

NSW Labor MP Trish Doyle raised the allegation using parliamentary privilege on Wednesday. Photo: NSW Parliament

Ms Doyle told state parliament an MP assaulted the woman “in a way she had not consented to” when they met at a secluded lookout at Yellow Rock.

Ms Doyle said the woman now felt “fear, hurt and anger”.

The ABC has spoken to the woman about Mr Johnsen’s alleged behaviour both inside and outside of NSW Parliament.

In his statement, Mr Johnsen said: “I am devastated by these allegations.”

“I have voluntarily spoken with NSW Police, and I have and will continue to fully cooperate with their inquiries.

“I am confident any investigation will conclude that I am an innocent party.

“Without admission, I have chosen to step aside from my parliamentary secretary role and will not sit in the Nationals party room nor the joint party room.

“I will be taking leave effective immediately for a short duration.

“As the matter is with the NSW Police I will make no further public comment.”

The statement came just one hour after the ABC sent questions to Mr Johnsen and Nationals Party leader John Barilaro about several  allegations.

In an interview with Nine Radio on Thursday, Mr Barilaro said he first learnt of the allegation at 7pm on Wednesday.

“I rang Michael at 7.20, to ask him directly,” he said.

Mr Barilaro said he subsequently spoke to the Premier and his own leadership team.

“This a very serious matter, I feel for all involved and I don’t think I could have done anything more or sooner [than] within a couple of hours having a statement from Michael and asking him to stand aside.”

Mr Barilaro said Mr Johnsen was “not in a great way”.

While Mr Johnsen has not resigned from the Nationals, he will not sit in party room meetings while the police investigation takes place, effectively plunging NSW’s Coalition government, which had previously had a one-seat majority, into minority.

Ms Berejiklian said that did not concern her.

“I think all of us want to make sure justice is served well and properly and the alleged victim needs to be able to have a processed where nothing is prejudiced, so I’m going to be really careful about what I say,” she said.

“I’m grateful that the police are investigating the matter and I think all of us want to get to the bottom of it.”

Commenting more broadly on recent allegations of sexual assault in politics, Ms Berejiklian said “we needed everyone working together to make change”.

“Otherwise this will be another ripple, people will forget about it and nothing happens, and I don’t want to see that.”

She said she hoped people would think about “culture, unconscious or subconscious bias and how we can respect each other”.

• For confidential support and services around sexual assault, contact 1800 RESPECT online or by phone on 1800 737 732. If you or someone you know needs help, contact Life Line on 131 114

-ABC