David Cameron has denied trying to "dictate" the terms of a Scottish referendum and has said the country's future must be decided by its people.
It is understood Downing Street may set a time limit for any binding vote, and insist it be a straight choice between leaving or remaining part of the UK.
Scotland's Deputy First Minister Nicola Sturgeon accused Westminster of "trying to interfere in Scottish democracy".
But David Cameron said he wanted the vote to be "legal, fair and decisive".
The Scottish National Party has pledged to hold a referendum in the latter half of its term, with 2014 thought to be the preferred date.
'Moral force' The UK government is expected to say that Scotland can hold a referendum on any subject it chooses but the result would only have advisory status.
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Were Scots to back independence, this would mark the beginning and not the end of a long, tortuous process of negotiation between the Scottish and Westminster governments ”
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Nick Robinson BBC Political Editor
It is expected to confirm that Westminster could give it the backing to hold a binding vote - but conditions are likely to be attached.
BBC political editor Nick Robinson said Westminster could formally lend Holyrood the legal power to set their own referendum conditions but such a move would usually come with a "sunset clause" attached - a time limit within which the extra power must be used.
It could also rule out a third choice in any vote - for greater powers to be devolved to Scotland without full independence - which Mr Cameron fears could split the unionist vote.
'Legal and decisive' Following Monday's cabinet meeting, the prime minister's spokesman said the 1998 Scotland Act, which brought about devolution, made clear that constitutional issues were reserved for Westminster.
"Clearly, a number of independent commentators and legal experts have highlighted the fact that a referendum Bill passed by the Scottish Parliament could be open to legal challenge," he added.
Mr Cameron told Sky News he wanted to resolve that "legal uncertainty" and wanted to
work with the Scottish government to give the people of Scotland the option of "a fair and more decisive question", put earlier rather than later.
David Cameron: "I strongly support the United Kingdom"
"But we're not going to dictate this, this is something we want to resolve, the legal position," he added.
But Scotland's Deputy First Minister Nicola Sturgeon accused Mr Cameron of "a blatant attempt to interfere" in a decision that should be for the Scottish government and Scottish people.
"It's the attachment of conditions that gives the game away - this is Westminster trying to interfere," she told BBC Radio 4's Today programme.
"Perhaps I should be relaxed about that because the more a Tory government tries to interfere in Scottish democracy then I suspect the greater the support for independence will be, but there is a key issue of democratic principle here.
"The SNP was elected on a clear prospectus and it's right that now that we have the mandate we can proceed on that basis."
'Absurd' In its 2011 manifesto the party did not suggest a date for a referendum, stating simply that it would bring forward its Referendum Bill "in this next Parliament".
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It's necessary for the people of Scotland to be given the opportunity to decide their constitutional future sooner rather than later”
End Quote Johann Lamont Scottish Labour leader But Ms Sturgeon said Mr Salmond had made it "abundantly clear that our position was to have a referendum in the second half of the parliamentary term" during the 2011 election campaign.
She called the idea of a sunset clause "absurd" and said referendums in the UK were always "consultative and advisory" so talk of a binding vote was unnecessary.
She also said the SNP would prefer a straight yes/no referendum, but there was "a significant body of opinion" in Scotland which was in favour of financial independence, but not full political independence.
The
Scottish government's website states that, even if a non-binding referendum was held: "The moral and political force of a vote for independence would be enormous, and impossible for a future government to ignore. A negative vote would similarly have a political consequence."
'Resentment' But Conservative peer Lord Forsyth, a former Scottish secretary, said the SNP had not set a firm date for a referendum because they knew the majority of people were currently opposed to full independence and "they are afraid they will lose it".
"They want to spend the next two or three years creating resentment on both sides of the border," he told BBC Radio 4's World At One.
"It is quite extraordinary that the party which stands for independence for Scotland won't take yes for an answer from David Cameron when he says the Scottish people can decide".
Chancellor George Osborne led discussions on Scotland at Monday's cabinet meeting and set out his concerns about the impact of uncertainty over a referendum on Scotland's economy. The PM's spokesman said both Mr Cameron and Mr Osborne had been told in private by business leaders that uncertainty was deterring inward investment.
Scottish Labour leader Johann Lamont told the BBC she agreed with the prime minister that a vote should take place "as soon as possible" on "a clear question".
"It's necessary for the people of Scotland to be given the opportunity to decide their constitutional future sooner rather than later in order that the uncertainty around the economy, around business and all the rest of it is addressed," she said.
taken from http://www.bbc.co.uk/news/uk-politics-16463961
