Nicola Sturgeon’s preference for holding another referendum on Scottish independence in the second half of next year has been put in doubt after the Electoral Commission recommended a gap of at least nine months between the completion of the required legislation and polling day.

Legislation to enable a second referendum was introduced by Sturgeon, the first minister, to the Scottish parliament in May. This could be completed by the end of 2019, but supporting legislation would then have to be passed to specify the details of the poll.

In a submission to the Scottish parliament’s finance and constitution committee, published last week, the Electoral Commission insisted it should be given 12 weeks to assess the wording of the question to be put in the referendum.

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Referendum wording has been the subject of some controversy, since the draft bill states the commission will not be consulted if it has previously assessed or recommended a question, as was the case with the yes/no format used for the 2014 referendum.

Critics argued the yes/no format favoured the affirmative side, and the commission subsequently recommended the options of leave and remain for the 2016 EU referendum.

While the commission said it had not ruled out a future yes/no question on independence, it believes the assessment should be based on current evidence and political context.

“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,” it wrote in the submission.

In terms of timetabling, the submission leaves the Scottish government with little room for manoeuvre.

The submission recommends taking 12 weeks to assess the question, including eight to carry out public opinion research and a further six for designating lead campaigners. It acknowledges this could overlap with the six-month period it recommends between legislation being passed and the start of a campaign.

The submission explains this six-month period “is so that campaigners and counting officers have sufficient time to understand, take advice on, receive guidance and generally prepare to comply with the rules once they are in force.

“Most importantly, it is this lead-in period that also enables voters to be informed about the issues at stake in the referendum and have confidence in the process leading to a free and fair referendum, with a result that has overall legitimacy for the public,” it added.

The submission recommends a minimum 10-week campaign period that, added to the 26-week lead-in period, amounts to 36 weeks or roughly nine months.

The parliamentary timing before this recommended lead-in period is also tight. The finance and constitution committee will take oral evidence on the bill during September and October and then publish its first-stage report.

Sturgeon has said she may consider accelerating the passage of the bill but, even if it is passed by Christmas, secondary legislation will be required to specify the referendum date, length of campaign period and the question itself.

The first minister has previously committed to securing the necessary transfer of powers from Westminster before holding a vote, and warned Boris Johnson this month against blocking a fresh referendum after a poll found a majority would now vote yes.

A Scottish government spokesperson said: “The referendums (Scotland) bill is scheduled to complete its parliamentary progress by the end of this calendar year, but it is always open to seek parliament’s agreement to an accelerated timetable. And while the timing of a referendum will be for parliament to determine, we will carefully consider all suggestions from the Electoral Commission.”