Two of the candidates seeking to be the next leader of the Scottish National party have described author JK Rowling as a “national treasure” despite her branding their predecessor Nicola Sturgeon a “destroyer of women’s rights”. Kate Forbes and Ash Regan who are vying with Humza Yousaf to become the next first minster, both described Rowling as “brave” when asked on a Sky News leadership debate on Monday evening about the Harry Potter author, who has made regular, often highly personal, interventions in opposition to Sturgeon’s gender recognition reforms. Asked if she disagreed with Rowling on transgender rights Forbes, who is on maternity leave from her role as finance secretary, replied “No I don’t disagree with her.” When asked if the author was a national treasure in a quickfire round of questions by presenter Beth Rigby, Yousaf, the Scottish government’s health secretary, said the author was “amazing in terms of the books she’s written, but I do disagree with her vehemently on the issue of transgender rights”. Polling conducted in advance of the debate found that most voters believed none of the three candidates would make a better first minister than Sturgeon, who announced her shock resignation last month after eight years. But the survey also found that 56% of voters said they opposed the gender recognition reforms “from what they had seen and heard about them”, compared with 26% who supported them. Forbes’ response in particular casts extreme doubt on the survival of the SNP’s governing partnership with the Scottish Greens should she be elected. Both co-leaders Patrick Harvie and Lorna Slater have been highly critical of Rowling’s stance and have already signalled profound concerns about Forbes views on other issues such as equal marriage and abortion. In the first televised debate since ballots opened on Monday morning, Forbes and Yousaf, the frontrunners in a contest that is thought to be too close to call, traded blows about what Sky’s polling suggested in terms of their appeal to different sectors of the electorate. Yousaf claimed that Forbes’ popularity had “plummeted” among SNP voters since the start of the campaign, when Forbes – a member of the evangelical Free Church of Scotland – first confirmed her socially conservative stance on a range of issues. Pressed by Rigby to apologise to “married couples with kids watching this, gay married couples watching this thinking that you disapprove of their lifestyle”, Forbes insisted: “I certainly, certainly don’t disapprove”. Stumbling slightly, she went on: “I mean, there are people in my own family and my job as an elected representative is to represent everybody without prejudice”. But Forbes went on to state that a gay man could consent to conversion practices. Asked about the Scottish government’s commitment to introduce a full ban on conversion practices, she made a distinction that “coercion is abhorrent”, but was then challenged on an expert advisory group’s finding that it is not possible for an individual to genuinely consent to such treatment. Asked about an adult gay man who wanted therapy to change his sexuality, she replied: “That’s his choice”. Yousaf told Forbes this showed she was “not able to give a really straight answer to a really straight question on our progressive agenda” and this was going to alienate SNP supporters. He told her: “You can appeal to conservatives because of the economic vision you’ve got but you’re not able to maintain the support that we’ve got.” Forbes retaliated that she was “more trusted on every policy area”, but Yousaf argued this was because she had not had a public service delivery role. “I’ve had three of the most difficult roles in government in the last 10 and a half years,” he claimed. Sky’s polling by YouGov suggested that all of the candidates had yet to convince voters. For all three, at least a third of voters didn’t know whether they’d make a good or bad first minister.