Nationals leader Barnaby Joyce is under intense new pressure following a call from backbencher Andrew Broad for him to stand down and an allegation that he sexually harassed a woman.

Broad said he would raise the leadership issue at Monday’s party meeting, saying that Joyce’s going to the backbench would be in the best interests of Joyce, the party and the government.

Meanwhile, a woman has made a complaint to Nationals federal president Larry Anthony accusing Joyce of sexual harassment.

Joyce strongly denied the allegation, saying it was “spurious” and “defamatory”, and went back to something 18 months ago.

“I ask the person to refer it to the police because I deserve my opportunity of defending myself,” he said.

After Broad’s salvo, the party’s Senate leader, Nigel Scullion, locked in behind Joyce. Its deputy leader Bridget McKenzie said: “There is no stronger advocate for regional Australia than Barnaby Joyce”.

But while Joyce earlier seemed to have shored up his position, there is now once again great doubt that he can survive. A self-justifying interview he gave to Fairfax defending himself appears to have backfired.

Eyes will now be on whether junior minister Michael McCormack signals he is willing to challenge Joyce. McCormack is considered the only viable alternative. He trailed his coat in a Sky interview earlier in the week, refusing to back Joyce multiple times before finally doing so.

Broad, who is the member for the Victorian seat of Mallee, on Thursday said in an interview on ABC Radio Statewide Drive Victoria: “It’s about having your mind clear to do the job”.

He said that at this point, Joyce’s “judgement is erred, he’s not thinking in a place where he can be put up as the acting prime minister of Australia. Some time out and hopefully some time to regroup and he may come back to make a further contribution.”

Broad, who spoke to Joyce before making his call, said he would be taking a resolution to the meeting from the local party members in his electorate saying Joyce should stand down.

He criticised Joyce for the high media profile he has adopted this week when he is supposedly on leave.

“He’s meant to be taking a break and he’s clearly playing to the media. You know, this is an issue that we should have let quietly die, and let’s get on with the core job but he’s not prepared to do that.”

Earlier – after the death of evangelist Billy Graham – Broad tweeted:

Scullion said: “If I was a betting man I’d think that Barnaby Joyce will still be deputy prime minister through the end of Monday”.

Scullion told the ABC he disagreed completely with Broad. “I’ve worked closely with Barnaby and I can tell you that right up to when he took leave … he had his mind completely on the job.”

“So we’ll get back on Monday and I hope and I trust that the National Party will return Barnaby to the leader[ship],” Scullion said.

“I have to say to Broado … he didn’t actually have to do that. I’m quite sure when Barnaby would have come in, let me tell you Barnaby is not a man who is afraid of democracy, so I suspect he would have come in and said by the way I’m going to spill my position just so you can all have a clear run at it,” Scullion said.

McKenzie said all Nationals MPs were welcome to bring issues to the partyroom. She also pointed out in a statement that Monday’s meeting would not be a full partyroom meeting, because of Senate estimates hearings.

Party sources noted there could not be a spill motion moved at that meeting. There would need to be a meeting of all 21 MPs for that to happen.

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.