The UK Government will only grant Scotland the legal power to hold an independence referendum if it rules out a second question on greater devolution, it has been confirmed.
Scottish Secretary Michael Moore said a single question ballot is "essential" if the UK Government is to give Scotland the legal power to hold the referendum.
The Scottish Government has said it is open to including a second question on further devolution, often called "devo plus" or "devo max", on the ballot paper.
Opponents view this as a fall-back option for the SNP to try to salvage something from the referendum if Scotland votes No to independence.
But Mr Moore rejected this option on Monday, insisting on a legally-binding assurance that Scotland will be asked a single question.
If no agreement is reached then the power to hold the referendum will not be devolved to the Scottish Parliament, he told the Commons Scottish Affairs Committee on Monday evening.
Holyrood and Westminster are currently negotiating the terms of the referendum.
Anything that is explicitly ruled out will be contained in the "section 30 order" — the legal instrument that will permit Holyrood to hold the referendum — while other non-binding issues will be contained in a separate "memorandum of understanding".
Conservative MP Simon Reevell asked whether a single question would be "a section 30 matter".
Mr Moore responded: "Yes. I think it is pretty essential that in transferring the power that we set out what that power is."
Committee convener Ian Davidson (Labour) asked what would happen if the parliaments could not agree on the section 30 proposals.
Mr Moore said: "Then the legislation is not devolved. This whole process has to be approved by both parliaments. Without that the law stays as it is at the moment."
He added: "The section 30 order would set out the terms by which the power would be devolved, over a single question and all of the other bits that we covered in the consultation.
"The section 30 order has to provide the legal framework for powers to be transferred which currently reside with this parliament.
"There are other aspects that do not require, necessary, the legal agreement between the two parliaments but are still politically important.
"So those are the issues that might be in the separate document outside of the section 30 order."
However, he confirmed that this separate "memorandum of understanding" would not have the same legal force as the section 30 order.
The Scottish Government insisted on Monday night that a second question on further devolution remains firmly on the table.
A spokesman for Deputy First Minister Nicola Sturgeon, who is now leading the Scottish Government`s referendum negotiations, said: "This is Scotland's referendum, and the arrangements for it should be made in Scotland, not dictated by Westminster.
"All of the relevant issues governing the referendum, including that of a second question, which has significant support among the public and civic society, must be determined in the interests of the Scottish people, not in the narrow interests of any political party.
"That is the spirit in which the Scottish Government is approaching the discussions that are currently under way with the UK government.
"We hope to make more progress in these discussions this week and we are optimistic of reaching agreement in the next few weeks."
Scottish Ministers have been pressuring Mr Moore to distance himself from comments Mr Davidson made during a controversial appearance on the BBC's Newsnight programme, where he insisted that the unionist parties would "of course" seek to attach conditions to the referendum.
Mr Moore told MPs on Monday night that "nobody envisages a blank cheque being handed over to the Scottish Government and the Scottish Parliament".
While he was firm on a single question, he said the possibility of extending the franchise to 16 and 17-year-olds was still up for debate.
He also confirmed that the timing of the referendum will be left to the Scottish Parliament.
Dundee MP Jim McGovern (Labour) said: "It would appear that almost everything is up for negotiation: the franchise, one question or two questions."
Mr Moore interrupted: "No. A lot of detail has not come forward yet from the Scottish Government about how they wish to deal with some of the central issues that are really important to us to make this a legal, fair and decisive referendum.
"But a single question is right at the heart of that. I hope I was clear on that."
Mr McGovern continued: "You were actually. We don't disagree on that, but one of the parts that we seem to have given up on almost from day one is an early referendum. We've never actually pushed that one.
"Although we have made noises and did some sabre rattling we seem to have given that up."
Mr Moore said: "Provided we can get this referendum sorted in a particular timescale, that we actually know there is an end point to this, then I think letting the Scottish Parliament determine it is a fair enough proposition."
The Scottish Government has proposed to hold the referendum in autumn 2014.
It remains to be seen whether the franchise will be prescribed in the section 30, or left open to the Scottish Parliament to decide.
Mr Moore said he hoped to have full terms of the section 30 order and the memorandum of understanding agreed before the Scottish Parliament autumn recess begins on October 22.
- Scottish Secretary urges First Minister to open up over independence
- Margo MacDonald calls on Alex Salmond to agree single referendum question
People who read this story also read
- Scottish independence is 'minority preference that 32% are in favour of'
- Tens of thousands of pounds of damage caused at car dealership
- Three-way split on Scottish independence in new poll
- Men due to appear in court after £10,000 of city centre vandalism
- Ferry routes continue to be disrupted by strong winds battering the north