Alex Salmond, Scotland's First Minister, has called on David Cameron to distance himself from "astonishing" claims by a party source that a 'Yes' vote would not automatically mean Scotland becomes independent.
In a furious letter to the Prime Minister, Salmond calls on him to rubbish the claims, attributed to a senior coalition source in Friday's Herald newspaper, that impossible demands in any post-referendum negotiations would not be met and that the "status quo" would be the default option.
Salmond said he was "astonished and disturbed" by the comments.
In the letter to Downing Street, he referred to the terms of the Edinburgh Agreement, which paved the way for a legally-binding referendum on Scottish independence to take place.
He wrote: "On 15 October 2012, you and I signed the Edinburgh Agreement. This was an historic accord, deeply rooted in our shared traditions of democracy and mutual respect.
"In particular, paragraph 30, pledging the signatories to 'a decisive and respected outcome' is, while the very least that our citizens would expect, something of which we both can be proud.
"It is against this backdrop, that I am so astonished and disturbed by the front page story in the Herald, and reflected in another paper, reporting that a 'senior coalition source' has briefed that a Yes vote would not guarantee independence.
"As you will understand this runs counter to the letter and spirit of the Edinburgh Agreement, and I urge you to distance yourself from this position as quickly, and as publicly as possible.
"Failure to do so will be interpreted, at best, as complicity, and, at worst, endorsement of this deeply anti-democratic position."
Salmond's letter to the Prime Minister came after a week in which all three of the main UK parties insisted they would not agree to a currency union between an independent Scotland and the rest of the UK. Such a set-up would be the Scottish Government's preferred option.
The First Minister's letter continued: "Of course this week has seen a series of sabre-rattling interventions from UK Cabinet Ministers supporting the Union, totally at odds with your comments last Friday at the Olympic Stadium.
"Leaving aside the boost these have given to the Yes campaign, you must realise the fundamental importance of our constitutional debate taking place against the backdrop of mutually agreed democratic processes.
"Any unrefuted suggestion that you had removed that guarantee, and unilaterally shifted the whole basis of the campaign (which you so consistently say you want to stay out of), would be an exceptionally serious matter.
"I urge an immediate clarification and better still an acceptance of the challenge for a head to head debate when our respective Cabinets meet in Aberdeen which would allow this and indeed other matters to be comprehensively put to rest."
Chief Treasury Secretary Danny Alexander, responding to the Herald report, has said that the UK Government will "totally respect" the result of the ballot on September 18.
''The result of the referendum will be respected, full stop, end of story," he told BBC Radio Scotland.
The source reportedly said: ''A Yes vote in the referendum would be the start of a process, not the end of one; we would start negotiations. But if Alex Salmond made impossible demands, we would not just roll over and agree to everything he wanted. If we could not reach agreement, the status quo would be the default option.''
A Downing Street spokeswoman said: "As the Prime Minister made clear in his recent speech, 'if people vote yes in September then Scotland will become an independent country and there will be no going back'.
"This is a decision that is for those in Scotland to make - it is their choice, their vote and the result of the referendum will be fully respected."
Stirling MSP Bruce Crawford, Convener of the Scottish Parliament’s Referendum Bill Committee, said: "From the Bedroom Tax to the privatisation of the Royal Mail, Westminster has imposed a series of damaging and unpopular policies on Scotland – but for the UK Government to suggest they could ignore the result of Scotland’s referendum takes the democratic deficit to new extremes.
"Two polls have shown that Westminster's attempts at bullying on the pound have simply moved more people towards voting Yes - when people in Scotland hear that Westminster is willing to ignore their democratic vote, even more will be convinced of the need for independence.
"The interventions from the Tories and their Labour and Lib Dem helpers are even more bewildering coming on the back of David Cameron’s call for the rest of the UK to ‘lovebomb’ people in Scotland. When it comes to Scotland it seems that the Westminster elite only has two settings – patronising or bullying.
"The No campaign has clearly been scared into making these threats as the polls narrow and the momentum is with Yes – but Westminster’s attempts at bullying won’t wash. People in Scotland can see through them and they only serve to highlight the growing necessity of having a government that works in Scotland’s interests, rather than against them."