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, 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.
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 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."