THE voting watchdog has insisted it must be allowed to scrutinise the question in a second independence referendum, upending SNP plans to reuse the Yes/No format of 2014.

The Electoral Commission told MSPs that it needed to test the intelligibility of any question before it was enshrined in legislation and put on the ballot paper.

It followed the Scottish Government, through its Referendums Bill at Holyrood, trying to avoid the Commission re-testing any question it had previously approved.

In practice, this is aimed at a single instance - the Commission’s approval of the Yes/No question “Should Scotland be an independent country?” five years ago.

Since then, the Commission has ruled against using the same format in case it advantages the Yes side, insisting on a Leave/Remain choice for the 2016 EU Referendum.

A change to Leave/Remain could be tricky for the SNP, which still campaigns for a Yes vote.

Last week SNP Brexit secretary Michael Russell told MSPs the 2014 format should be retained for “clarity and consistency” and it would be “very confusing to change it”.

However Dame Sue Bruce, the Electoral Commissioner for Scotland, told the finance committee that any question must be tested.

She 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 to provide confidence and assurance 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 standard testing procedure would take up to 12 weeks, with the bulk of the time used for research with the public, including focus groups and in-depth interviews.

The Commission would also take advice from experts and undertake a consultation when considering the question, before publishing a report supplied to ministers.

Chief executive Bob Posner said the Commission would start with an open mind.

He said: “I think it's really important to say that we don't start with a preposition at all.

"The fact that there was in 2014 a referendum in Scotland, if we had a repeat of that referendum, it would be a very material consideration that there was a question that was in the public's minds back then and there's a familiarity, and polling since. So all that would be picked up as part of the assessment process but we wouldn't start with any position at all."

He added: "No-one should think that just because there's been a 2016 referendum where Remain and Leave was used, there would be any reason why that would be relevant or appropriate for another referendum, or not as the case may be."

Head of the Electoral Commission Andy O'Neill said allowing it to test the question would mean people would be able to focus on the issues of the debate, rather than discussing the question itself.

He said: "We believe context can change, it may not change, we don't know that until we've done the question testing and given you the advice.

"I think one of the things you get from our expertise is confidence in the question and I think people - the voters, the campaigners - can have confidence if we provide a good product in terms of the advice.

"You can choose to accept it or not but we give you our advice.

"That confidence brings acceptance and it brings acceptance from the voter and the campaigners so you can then go off and debate the issues rather than the question."

Pamela Nash, chief executive of Scotland in Union, said: “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.”

The Referendums Bill is designed to create a general framework for referendums.

However it is aimed primarily at paving the way for Indyref2 next year, if the UK grants Holyrood the required powers for a new vote.