The Electoral Commission has also set out a year-long timeframe for holding a second vote on leaving the UK that appears to make the First Minister’s hopes to stage a poll late next year increasingly forlorn.

The Scottish Government has published legislation at Holyrood to pave the way for a second referendum but the commission calls for a series of changes to be made in key areas, including the proposed question, in a submission to Holyrood’s constitution committee.

The watchdog warns: “The Electoral Commission must be required to assess any referendum question proposed in legislation, and set the commission’s views before the Scottish Parliament, regardless of whether the commission has previously published views on the question proposed.”

The Electoral Commissions submission suggests time is running out for Nicola Sturgeons preferred timeframe of late next year for a second independence referendum. Picture: John Devlin

What question will be put to voters has been contentious since the Referendums (Scotland) Bill was published in May. The bill said that, if the proposed question had already been assessed by the commission, it should not have to be assessed again.

This would exclude the commission’s involvement in the same question as 2014 – “Should Scotland be an Independent Country?”

The commission has since ruled out a Yes/No question in the Brexit referendum, instead recommending a Remain/Leave question. This was found to be more balanced after fresh evidence was taken.

A change from Yes/No to a Leave/Remain question could damage the pro-independence movement, with the Yes campaign widely seen as having been successful in conveying a positive message in 2014.

In its submission to MSPs, the commission says: “At any referendum it is essential that voters can easily understand and answer the question and any statement which precedes it on the ballot paper.

“The intelligibility of the referendum question is fundamental to voters’ ease of understanding and participation in the referendum and underpins the legitimacy of the outcome.”

Although not obliged to accept the recommendations of the commission, it would be politically difficult for the SNP to forge ahead with plans for a second referendum without the endorsement of the independent elections watchdog.

The Scottish Government would also need authorisation from Westminster through a Section 30 order to stage a second referendum. It may be that a future UK government inclined to grant a Section 30 order would withhold it until the Electoral Commission’s views are respected.

Ms Sturgeon’s hopes of staging the referendum late next year were undermined by a timeframe of at least nine months set out by the commission. This would include a 12-week period for the watchdog to assess the question and provide a view on it before legislation or regulations are passed. The legislation should also be passed six months before the final ten-week referendum period, when rules around campaigning and spending apply.

It suggests time is running out on Ms Sturgeon’s preferred timeframe of late next year for a second referendum, with the legislation itself yet to be formally passed at Holyrood.

There are also concerns over the risk of foreign companies using UK subsidiaries to fund referendum campaigns in Scotland with money that comes from outside the UK.

The commission wants better information about campaign spending recorded by participants, and powers to impose fines of £500,000 instead of the £10,000 proposed in the bill.

A Scottish Government spokesperson said the legislation makes “specific provision” for the involvement of the commission to consider the proposed referendum question. The concern centres on “repeat testing” of questions that have already been found to be intelligible.

He added: “It will be for Parliament as a whole to decide and vote on these matters – both the proposals in the bill and in any regulations made under it – and we will of course listen to all views put forward.

“ The 2014 referendum question was proposed by the Electoral Commission and provides clear precedent for a simple, straightforward and understandable question.”

Pamela Nash, chief executive of Scotland in Union, said the Scottish Government must respect the views of the elections watchdog.

She said: “If MSPs press ahead with the bill, it is vital that this important recommendation from the Electoral Commission is actioned.”

“Should we ever be in the situation where Scotland’s place in the UK is subject to another referendum, to ensure that it is carried out fairly and the result is respected by all, the wording of the question must be looked at again by the Electoral Commission in all circumstances, including if the question proposed is the same as in 2014.”

Electoral watchdog insists on assessing any indyref2 question before it is put to voters