Kate Forbes shrugged off a backlash from within the SNP to stand by her scathing criticism of rival leadership candidate Humza Yousaf, saying Scotland needed a leader with “guts”.

The Finance Secretary surprised many of those watching the debate on STV as she lambasted Mr Yousaf’s record in three Cabinet posts and even described her own government’s performance as “mediocre”.

During the debate she said to Mr Yousaf: “You were a transport minister and the trains were never on time, when you were justice secretary the police were stretched to breaking point, and now as health minister we’ve got record-high waiting times. What makes you think you can do a better job as first minister?”

Mr Yousaf replied by saying Ms Forbes would drag the party to the right and could not be trusted to stand up for the Scottish people.

The ferocity of Ms Forbes’ attack suggested an undercurrent of division in the party and prompted a backlash from insiders who fear that more outbursts in three further TV debates will undermine faith in the SNP.

SNP ministers have said they would have a “serious problem” serving in a Kate Forbes government. One called Forbes’s attacks “reprehensible and hugely disappointing” and said it was insulting to long-serving party politicians and activists.

Another, Shona Robison, the social justice secretary and one of Sturgeon’s closest allies, told the Daily Record that she would have to think long and hard about serving under Forbes. 

“I think it’s about the tone and when that steps into what you could describe as a bit of a trashing of the collective record of the SNP government, [it] does not sit well with SNP members,” she said.

The leadership squabble comes on the back of a poll by Redfield and Wilton Strategies conducted between 2 and 5 March showing support for a Yes vote fell by seven points to 42% while the number of undecided voters increased by three points to 8%.

Speaking after a tour of the Scotch Whisky Experience in Edinburgh Ms Forbes stood by her comments.

“This is an election contest to be the next First Minister and I think the public and SNP members want to see somebody who has the guts to recognise what needs to change, and also recognise the fact that we need to have a plan to deliver.

“Last night was all about having the candour and the honesty to say that more of the same isn’t what Scotland needs. We actually do need change.

“But secondly, it was about competence, and if any SNP leader and future First Minister is going to be taking on the Tories in Westminster, for example, then they need to have the mettle and they need to have the courage to do that, and I think that was what was on display last night.”

Ms Forbes repeated her message during the TV debate that “more of the same won’t cut it”, adding: “We do need an honest and grown up debate, and I think the SNP is big enough and brave enough to have that adult debate about what the future holds.

“If we can’t have robust exchanges about the future of our economy, the future of our public services and how we deal with the issues that are of profound significance to Scotland, then that leaves the question of how healthy the democracy is.”

Ms Forbes indicated there was more dissent in the Cabinet by using her visit to the whisky centre on the Royal Mile to confirm her support for the drinks industry and her opposition to her government’s proposed ban on alcohol advertising.

“There has been a strong commitment to reducing alcohol misuse, but we have to look at the impact of this on business.

“We need to sit back and give businesses a bit of breathing space.

“We should not be banning alcohol advertising.”

On business costs, she said: “I support higher taxes to invest in public services but I would like to be in a place with faster growth and therefore a more attractive tax regime.”

Nicola Sturgeon was asked about the attacks on her government and said: “We have a record in government to be proud of.

“I think what all candidates need to do — and I think all candidates are doing — are setting out how they will build on that and take that forward. But I don’t think they need help and advice from me in doing that.”

Asked if she thought Mr Yousaf had failed at transport, justice and health, as Ms Forbes alleged in the TV debate, Ms Sturgeon said: “I think all of my ministers have done a good job.”

What they said: The STV debate