The SNP has drawn up transitional plans for independence despite polls showing support for the move has dropped to around a quarter of Scots.

The paper, titled 'Scotland's Future: from the Referendum to Independence and a Written Constitution', envisages a Scottish Independence day as early as March 2016.

Elections to an independent Scottish parliament would follow in May.

The plans coincide with the lowest levels of public support for independence since devolution.

A report by Scottish Social Attitudes in January found only 23% of voters in favour, down from 32% last year.

Scottish deputy first minister, Nicola Sturgeon said: "Our proposals, set out today, would see this platform put in place immediately prior to the Scottish Parliament elections, to provide the newly-elected Scottish Government with the full range of powers it needs to develop the country.

"Today's paper provides the people of Scotland with a clear road map as to how Scotland would make the journey from a devolved system of government with the levers of power retained at Westminster, to a nation in which the powers of our national Parliament are complete and in which the people are sovereign."

A written constitution would be drawn up by the first parliament and could possibly outlaw "weapons of mass destruction".

Scottish Liberal Democrat leader Willie Rennie MSP said in a statement: "The SNP have hopelessly underestimated the scale and complexity of this.

"They would have to negotiate over 14,000 international treaties, a currency, the division of assets, membership of NATO and the host of international organisations.

"To say they will bang all this through in just 16 months is absurd. This will give most people in Scotland the shivers and fuel suspicion that the SNP are just making it up as they go along."

The SNP plans may also seem a little premature to prime minister David Cameron who said last week he would not ''pre-negotiate Scotland's exit from the United Kingdom".

Last month Scottish secretary, Michael Moore, accused SNP ministers of trying to "fast forward through the difficult bits" of the debate.

He accused SNP ministers of ignoring the substance of what a future independent Scotland woud look like by focusing solely on the yes/no vote.

A number of crucial issues such as EU membership, defence and fiscal separation still surround the independence debate.

This was highlighted last month when Sturgeon was unable to give details on arrangements for an independent intelligence gathering agency to the Commons foreign affairs select committee.

David Lidington, the Minister for Europe, accused the SNP of having not “thought it through”.