The SNP must understand why 30,000 members left the party in just over a year, two of the contenders to succeed Nicola Sturgeon have said.

Membership figures released after pressure from all three candidates in the race showed the drop between the last published figures and the beginning of the leadership contest.

A row ensued over the numbers, leading to the resignation of chief executive Peter Murrell and head of communications Murray Foote over incorrect comments made to journalists who asked about membership last month.

Speaking during a debate on Monday on LBC Radio, Health Secretary and contender Humza Yousaf said it would be for a new leader to find out why so many have left the party.

“First of all, the new leader, one of the first things they have to do internally is get in amongst the weeds and understand why we lost those members,” he said.

“Is it because, for example, people don’t view we’ve made enough progress on independence and been talking too much about process and not enough about policy?”

Asked the same question, former community safety minister Ash Regan said: “I’ve been obviously talking about this over the last few weeks, and I was the first to say, as part of this hustings, that I suspected that we had lost a large number of members over the last wee while.

“Obviously it’s anecdotal, I don’t have the data on this, I imagined the party perhaps does keep data on the reasons that people give when they relinquish their membership, but my assessment of it was it was just down to a lack of perceived progress on the independence question, and also the gender recognition reform.”

She added: “When large numbers like that leave, I think the sensible thing to do is to look into that and say, ‘why are we losing members and what can we or should we be doing about it?’

“I’m the only candidate here that set out an SNP action plan when I first announced my candidacy several weeks ago, the idea behind that being that we need to make members feel valued, we need to reflect the interests that they have, we need to modernise the party and bring back the democracy that I think is missing.”

Ms Regan went on to say some people had written to her since she announced her candidacy to say they would re-join if she became first minister, adding that “they consider me to be the only hope for the party at this juncture”.

Elsewhere in the debate – a much more collegiate affair than some of the more heated clashes throughout the leadership race – Kate Forbes said she would not want to see any more divergence between Scotland and the rest of the UK on tax if she won.

The Scottish Government is now able to set income rates and bands, creating differences north and south of the border which, given recent Scottish Government decisions to move in a more progressive direction, has caused some worry over people moving out of the country.

Asked by Mr Yousaf if she would “rule out people who earn a six figure salary like you, like myself, you would rule out they should pay any more tax than they currently do?”

Ms Forbes said: “I would rule out any greater divergence with the rest of the UK.”

The question was asked, the Finance Secretary said, against the backdrop of tax increases in the most recent budget, which she said she would like to see “embed”.

Ms Forbes also took the opportunity to retreat from her attack on Humza Yousaf during the first televised debate, when she said there was a place for him in her government, but “not at health”.

She said the comment was meant to be “tongue in cheek”, adding: “I can only say to Humza he knows how much I respect him and value him as a colleague.”

The candidates were also able to find common ground in the debate, with all three committing to removing the Trident nuclear weapons systems from the Clyde, joining Nato as an independent country and adhering to the defence bloc’s decree that 2% of GDP should be spent on defence.