Barnaby Joyce has revealed he campaigned to hold the seat of New England for the government during last year’s byelection in the full knowledge he would have to stand down as leader of the National party and deputy prime minister – yet he repeatedly refused to disclose any details about his private life.

Joyce’s partner, Vikki Campion, also accused unnamed people in the National party – identified during a television interview aired on Sunday night only as “they” and “conservatives” – of attempting to pressure her to terminate her pregnancy, advising her if she refused “they’re going to come after you”.

She said she had contemplated having a termination, but could not go through with it.

Joyce caused a political storm by accepting a payment from the Seven Network of $150,000 for the interview. Joyce went on medical leave last week in the middle of the furore, amid growing speculation about his future in politics.

The couple refused to answer questions during the interview about precisely when their relationship started and Joyce shut down questions about a public confrontation between Campion and his former wife of two decades, Natalie.

Joyce was not asked when it was that he revealed the relationship to colleagues in the government.

But Joyce said more than once in the interview that as soon as he was aware Campion was pregnant “I knew the day would come where I’d have to step down”.

Despite being aware of that eventuality, he did not publicly disclose the relationship nor the pregnancy during last year’s byelection contest despite being questioned repeatedly by journalists about his private life.

The first time Joyce acknowledged publicly that his marriage had ended was during the debate on legalising same-sex marriage after he defended the seat for the government last year.

On Sunday night he criticised Malcolm Turnbull for being publicly critical of his conduct, and acknowledged that he hung on to the leadership of the Nationals in part out of “spite” when the controversy about his relationship with Campion sent the government into a crisis this year.

He said he was much more concerned about the impact of the relationship and the pregnancy on his former wife and their four daughters than he was about the political consequences of his actions. “To be quite frank, I couldn’t give a shit about the political ramifications, really,” he said.

Joyce attempted to shield his partner from responsibility for the breakdown in his marriage by noting “I’m the adult”. There was a brief pause before she noted: “I am an adult too.”

Joyce was also contradicted by Campion when he recounted his decision to tell a journalist it was a “grey area” whether or not he was the biological father of Campion’s son.

Joyce said his observation was “actually a decision we made together”. Campion begged to differ: “I didn’t say use the words grey area.

“Uh, I was ... I was deeply hurt by the grey area headline. Definitely”.

Government colleagues were bracing for the political impact of the interview. Joyce has been the subject of speculation about his political future. Last week the person who replaced Joyce, Michael McCormack, told the Conversation whether he would contest the next election was “a matter for him and that’ll be a matter for the National party in New England”.

“That’ll be a matter for a branch to nominate him and then that’ll be a matter for the branch members in New England as to whether or not they decide if he nominates or if anybody else nominates,” he said.

“Then it becomes a preselection process as to who they think would best represent them going forward.”