The former One Nation senator Brian Burston has denied allegations that he sexually harassed a staff member and retaliated against Pauline Hanson, his former party leader, by accusing her of making unwanted advances towards him.

After Hanson used a speech in the Senate on Tuesday night to accuse an unnamed senator of “serious sexual harassment”, Burston confirmed that he was the politician involved.

But Burston has since hit back at Hanson by accusing her of sexually harassing him, claims the One Nation leader has rubbished as untrue and laughable.

Tensions appeared to reach breaking point when Burston was involved in a physical clash with Hanson’s adviser James Ashby in Parliament House in Canberra on Wednesday night. The pair’s altercation near the great hall was captured on video, and Burston appeared with a bandaged hand in the Senate on Thursday.

Burston claims Ashby approached him as he and his wife were leaving a function. He claims he was injured when he tried to grab a phone Ashby was waving in his face.

“I told him to fuck off,” Burston told News Corp. “I lost it.”

Guardian Australia has seen a complaint of sexual harassment made against Burston late last year, as part of a settled unfair dismissal claim. The complaint alleges that Burston made an inappropriate advance on a distressed staff member. She said he had asked whether he could “‘fuck’ me to make things better”.

“I refused his approach, but inside my world shattered,” she said.

A spokeswoman for Burston denied that the senator propositioned the staff member, stressing that a 70-year old man would not use the word “fuck”.

Asked if the former staffer had lodged a Fair Work Commission complaint, the spokeswoman replied: “No comment.”

Burston interjected that the allegations were “all bullshit” and “garbage”. He said Hanson – whom he described as “a woman scorned” – was engaging in payback because he left One Nation over other issues, including the party’s stance on company tax.

Burston’s wife, Ros, corroborated the denial of Burston’s spokeswoman. “My husband never says fuck,” she said.

Hanson’s Tuesday night speech accused an unnamed senator of sexual harassment and said the matter was “under investigation” by an unnamed entity.

“What is disappointing is that this parliament has allowed the horrible treatment of staff to continue without this senator being forced to go through some form of training to prevent poor treatment of his employees,” Hanson said in the Senate.

Burston’s spokeswoman said to expect a “bombshell” on Thursday evening in the Senate adjournment debate, when Burston is expected to take aim at the Hanson and her One Nation colleague Peter Georgiou.

Burston told News Corp on Wednesday night that one of the reasons he had left One Nation was because of sexual harassment from Hanson.

“Right back when we had our first One Nation AGM at the Rooty Hill RSL [in 1998], that was the first time she hit on me,” he said.

He claimed that Hanson “rubbed her fingers up my spine” while listening to the national anthem and she had propositioned him after he was elected in 2016, at her home in Queensland and in Canberra.

Hanson dismissed the accusations. “I’m 64 … but I tell you what, I’m not that desperate,” she told Sky News.

Burston and Hanson fell out bitterly before Burston left One Nation last June. The tensions manifested months earlier when Hanson picked Malcolm Roberts as the party’s No 1 Senate pick in Queensland. Burston split with his leader on the government’s company tax cut bill, a move she saw as a stab in the back.

He eventually quit the party to sit as an independent, and is now aligned with the United Australia party.