Britain's government will set out plans in the coming days to give Scotland more autonomy on tax, spending and welfare.
The move will come if Scotland rejects independence in a referendum on 18 September.
The British finance minister George Osborne said this in response to a poll which suggested voters were in favour of Scottish independence.
The poll is the latest evidence of a dramatic surge for the "Yes" Scotland campaign, which has seen it overturn a 22-point deficit in just a month.
Support for independence is said to have soared four points in a week while "No" dropped by the same number.
Mr Osborne said: "You will see in the next few days a plan of action to give more powers to Scotland."
Mr Osborne said the changes would be put into effect the moment there is a "no" vote in the referendum.
He said the plan was being agreed by all three major political parties in the British parliament.
Ed Balls has also given voters a personal guarantee there will be a "big transfer of financial powers" to Scotland if they reject independence.
The Labour MP made the pledge as he called on the Scottish first minister, Alex Salmond, to "be clear with Scots about what his plans for independence mean", warning leaving the UK could lead to significant spending cuts.
Mr Ball’s comments have been criticised by Linda Fabiani of the Scottish National Party who branded the pledge as "yet another panicked response from a 'No' campaign in complete disarray".
Ms Fabiani added: "As more and more people in Scotland wake up to the opportunities of 'Yes', the Westminster establishment is growing increasingly desperate."
In a move to further drive the "No" vote Ed Miliband will speak at the TUC General Council dinner tomorrow.
The Labour leader is expected to argue that voting against separation from the UK will make for a stronger Scottish parliament with more powers guaranteed.
A number of unions have already signed a joint statement "declaring that strength comes from staying together and that separation would damage the rights and conditions of working people."