Scotland’s finance secretary, Kate Forbes, declared her candidacy to replace Nicola Sturgeon as SNP leader and First Minister, but potentially scuppered her campaign after saying she would have voted against same-sex marriage had she been in parliament at the time.

The MSP for Skye, Lochaber and Badenoch is cutting short her maternity leave to take part in the contest against the Health Secretary Humza Yousaf and former Safety minister Ash Regan.

Ms Forbes, who has been a clear favourite, promised to be a “unifier” and someone who has “a grip on our economy”. She later qualified her comments on same-sex marriage buy saying she would attend a wedding and would protect gay rights.

However, her comments created some disquiet among the SNP ranks with some believing she has damaged her chances of succeeding Ms Sturgeon.

Richard Lochhead, the Fair Work Minister, tweeted that he had supported Ms Forbes entering the race but said he could not support a leader who would vote against same-sex marriage.

Ms Regan has also signalled a dissident view in the party by coming out equivocally for the oil and gas sector.

“I will not support an accelerated net zero path which sees us turn off the North Sea taps, throw 10s of 1000s of oil workers out of jobs, hollow out NE & H&I communities whilst still using and importing hydrocarbons,” she said. “I will stand up for our oil workers and their communities.”

Earlier, Angus Robertson, the Constitution Secretary, ruled himself out, saying that “as the father of two very young children, the time is not right for me and my family to take on such a huge commitment”.

He joins Deputy First minister John Swinney and Justice Secretary Keith Brown among those who will not be taking part.

The contest follows an Ipsos poll last Friday which showed that more than half of the public (54%) and SNP voters (51%) believe that Nicola Sturgeon’s resignation will have a negative impact on the case for Scottish independence.

The Ipsos survey of 1,513 adults, conducted on the day after Ms Sturgeon announced her resignation, found that 31% believed that Ms Forbes would do a good job. However, a third (32%) said they don’t know who she is.

Ms Forbes maintains her lead among 2019 SNP voters, of whom 44%, said she would be the ideal new leader and First Minister.

There is concern, however, that she may be a divisive figure. Her faith as an active member of the Free Church of Scotland put her at odds with Ms Sturgeon over the gender recognition law.

She had signed a letter urging a delay to the legislation, which will allow 16-year-olds to change gender. Ms Forbes was absent on maternity leave when the legislation was pushed through parliament.

There is talk that she may want to review the partnership with the Greens who backed the gender reform but opposed the freeports whose establishment in Scotland were a result of negotiations in which Ms Forbes played a key role.

Mr Yousaf launched his campaign in Clydebank stating that his late grandfather arrived in Scotland from Pakistan in 1962, speaking very little English.

“I don’t imagine in his wildest dreams that his grandson would one day be running to be first minister of Scotland,” Mr Yousaf said.

“It speaks to us as a nation that anyone, regardless of race, can aim for the highest office in our country and not be judged by the colour of their skin”.

The Ipsos survey had indicated that John Swinney, the Deputy First Minister, shared the same level of support as Ms Forbes, polling the highest of any potential candidate among 2019 SNP voters, with 47%.

However, he subsequently stated that he will not stand and is expected to support Mr Yousaf whom 20% said would do a good job, while 37% thought he would do a bad job.

Joanna Cherry and Stephen Flynn, who were among others polled, also ruled themselves out.

Three in five (61%) said that Ms Sturgeon’s resignation will have a negative impact on the SNP, while just 19% said it will have a positive impact.

The pattern is similar among 2019 SNP voters, with 61% thinking her resignation will have a negative impact on the party and 17% that it will have a positive impact. 

Reflecting on Ms Sturgeon’s time as First Minister, three in five believe she has changed Scotland for the better (59%), against a third who say for the worse (31%). Fewer than one in ten (8%) think she has made no difference.

Meanwhile, opinion is split on Scottish Labour leader Anas Sarwar who three in ten think would do a good job (30%) but a similar proportion say a bad job (29%).

Scottish Conservative leader Douglas Ross received unfavourable reaction with three in five (58%) thinking would do a bad job, against only 14% believing he would do a good job.

Comment: Battle to win the younger generation game