The Barnaby Joyce saga has taken another bizarre turn, with the former deputy PM speaking out three times in as many days on the possibility he might not be the biological father of his lover’s child.

Mr Joyce’s determination to keep breathing life into the scandal appears to be hurting not just the government but also his boss. Sunday night’s Newspoll was, as expected, Malcolm Turnbull’s 28th straight loss since taking the Lodge. But it also contained a nasty surprise: another three-point hit to Mr Turnbull’s once-unassailable title as most preferred PM, leaving him with a bare 37 to 35 per cent lead over Labor leader Bill Shorten.

Earlier on Saturday, Mr Joyce, the man causing the political pain, responded to apparent rumours circulating in Parliament by telling Fairfax Media the question of who fathered the child was “a grey area”. His pregnant partner and former media adviser, Vikki Campion, was reportedly present for the interview.

A day earlier, he told the paper he would care for the baby “even if” the boy was not his.

“It’s mine, on the record, there it is,” he said.

“And can I say, even if it wasn’t, I wouldn’t care, I’d still go through this, I’d still love him.”

After the interviews drew intense criticism, Mr Joyce again spoke out on Sunday to defend his public questioning of the child’s paternity.

“This issue has continued to be pursued by media despite my resignation, with paparazzi waiting for us at our gate at the airport on Friday and an upcoming appearance by a Daily Telegraph journalist on ABC’s Q&A on Monday night,” he told Fairfax.

“Media had also made requests around the issue which was printed today. Therefore we felt we had no choice but to tell the story.

“Despite a flood of other allegations by media and political types being used as a proxy to attack us for being together, none of those allegations has been proven true.”

Prime Minister Malcolm Turnbull on Sunday declined to be drawn on the comments, while former federal senator and now SA-Best leader Nick Xenophon urged Mr Joyce to “shut up” and “get on” with life.

“The matters that are in the papers today relating to Barnaby and Ms Campion are matters for them to resolve,” Mr Turnbull said.

Mr Joyce also claimed the Daily Telegraph, which broke news of his affair with Ms Campion, had never asked whether he was the father of the child.

But the reporter who wrote the story disputed that on Sunday, tweeting a screenshot of an email sent to the former deputy PM’s spokesman asking if Mr Joyce was “the father of the baby”.

Barnaby on the backbench

Seeking a “circuit breaker”, Mr Joyce quit the Nationals leadership last month amid ongoing scandal over his affair with Ms Campion.

He was also under pressure over an allegation of sexual harassment, which he denies, and over government jobs handed to Ms Campion.

Despite heading to the backbench, Mr Joyce has not stepped out of the spotlight, speaking to media outside Parliament and giving a sit-down interview with a rural newspaper last week.

“People come up and they say the same thing all the time, ‘mate that was a witch hunt’ and I agree with them,” he told Farm Online.

“Where’s the allegation that was ever proved? The tactics were really quite simple – throw enough mud and something’s bound to stick.”

Speaking to reporters outside Parliament, he failed to rule out a leadership comeback.

“I never rule anything in or anything out, right, because otherwise later on in life you look like a hypocrite,” he said, though he added he did not expect to return.

Mr Joyce also gave his first speech from the backbench last week, extolling the virtues of country-of-origin food labelling and laying out his policy priorities in his new role, which he noted had come “with a pay cut”.