Giving evidence to the Scottish Parliament's finance and constitution committee, Bob Posner, chief executive of the Electoral Commission said he did not think it right that "any politicians, any individual, academic, or anyone, should take the view 'I know the answer. I know this is clear in 2019. I know voters will understand that it's the right question'.
He added that whatever the question asked, it was "so core to the function of a referendum" that it was "prudent" it should be assessed, and that while the question asked in the 2014 referendum was tested at the time, "one shouldn’t draw any conclusions about what we would be saying now."
He added: "We will always look at the best way at the time to assess the question, taking into account material considerations, then we will publish all that, all the information and everyone can see it."
Mr Russell has said that a fresh Scottish independence referendum should use the same question as 2014 because it is still "current" and would avoid "confusion" among voters - effectively freezing the Electoral Commission out of the process of assessing the question.
However, Head of the Scotland office of the Electoral Commission, Andy O'Neill, said that testing "would give the electorate confidence in the question, no matter the result."
He said: "We do testing on a case by case basis, no precedent is set. We do the testing, collect the evidence, give you our advice. We have no preconceived ideas on that. The question, in terms of an independence question, has become part of the debate - we want to test that so the electorate have confidence in it and accept it."
Asked by Scottish Greens MSP, Patrick Harvie if the words "Leave and Remain" could ever be used again in a referendum, as they had "changed so profoundly in the aftermath of the 2016 EU campaign", Dame Sue Bruce, Scotland's Electoral Commissioner, said: "That is the kind of material that would be tested.
"Of course there will be new electors who were not voters in 2014 and who are new to elections and referenda and so forth, so the idea would be to test the question, to ensure that it's understandable and not nuanced on either side and that the electorate felt confident that they could participate in the referendum and cast their view appropriately in light of the question."
Mr Posner added: "In 2014 the Scottish Government did propose a question which it presumably thought was the right question, and fair, but we recommended a change and it was accepted. It was looked upon as the gold standard, that referendum, and I assume going forward in any other you want to continue any referendum to be the gold standard why would you introduce a risk in the system?
"Yes, we might end up with exactly the same question but you would want it to be tested - that's what we're suggesting."
"There's a category of question which is extremely important - it is a question which is not an old question, but a current question. In my thinking the question which was asked in 2014 remains a current question. It's a question which was approved in 2013 by the Electoral Commission.
"That question was used up until 2014 in every opinion poll and it's been used since then in over 50 opinion polls on independence.
"There is an issue of clarity and consistency - if a question is current and is in current usage, then why would you change it? It would be very confusing to change it."
However, today Dame Sue Bruce said: "We strongly believe that the Commission should be asked to test the question. Putting the voter at the centre of the process, we think a formal testing of the question helps provide assurance and confidence to the voter and to the Parliament posing the question, in terms of the integrity of the process to establish that it is clear and transparent and neutral in its setting.
"The provisions in the Bill should require us to test the question and there should not be a caveat excluding a question that's already been put."
Testing of referenda questions by the Electoral Commission can take up to 12 weeks using focus groups and in-depth interviews across Scotland. Advice is also taken from accessibility experts, plain English experts, and the final report goes to government ministers and the Scottish Parliament.
Mr Posner added: "We wouldn't start with any position at all. There will be a proposed question for us to assess - we wouldn't start from whether that was right or wrong, we would test it."
Asked directly about Mr Russell's stance, Mr O'Neill said: "We would argue that our expertise lies in question assessment. We believe context can change, they may not, but we don't know that until we've done the question testing. What you get from our expertise is confidence in the question.
"You can choose to accept our advice or not, that confidence gives acceptance from voters and campaigners so you can then go off and debate the issues rather than the question. That's why we think question testing, whether we've tested it five, six or 100 years ago, is important."
Reacting to the Electoral Commissions remarks, Pamela Nash, chief executive of Scotland in Union, said: “Polling shows that only one-fifth of people in Scotland support the SNP’s undemocratic plan to block independent analysis of any future referendum question.
“There shouldn’t be another referendum as it would lead to economic turmoil and deeper division, but - if there ever is one - it’s vital that it’s legal and fair, and doesn’t have a rigged question chosen by the SNP.
“The Electoral Commission has said that yes/no questions are unfair, and recommended a remain/leave question in the EU referendum.
“But this Referendums Bill is taking up parliamentary time that could be better spent on focussing on how to improve public services in Scotland - not ways to create more division.”