Edinburgh – Scottish First Minister Alex Salmond has unveiled formal consultation on blueprint for vote on ending political and economic union with England giving detailed timeline and proposed referendum question and suggesting May 2016 as the target to a post-UK parliament in Edinburgh.

The first minister said Wednesday the vote that will determine the future shape of the UK in the autumn of 2014 would be a “short, straightforward and clear” question to Scotland’s four million voters: “Do you agree that Scotland should be an independent country?”

The question will appear on the ballot unless talks with the UK Government, aimed at making the poll legally watertight, break down, said Salmond presenting the government consultation paper to Holyrood.

If that happens, the SNP Government will revert to a more complicated wording in a bid to avert a court challenge.

Salmond also kept the door open for a second question on devolution of more powers for Holyrood.

In a speech to members of the Scottish Parliament (MSPs) earlier, Salmond said: “The Scottish Government’s position is for independence. Therefore, that option will appear on the ballot paper in a straightforward manner.

“If there is an alternative of maximum devolution which would command wide support in Scotland, it is only fair and democratic that option should be among the choices open to the people of Scotland.

“We will not, as the UK Government seems to want, eliminate that choice simply because it might be popular.”

The vote is to be “the most important decision by the people of Scotland in 300 years”, Salmond said.

In a rare sign of political unity between London and Edinburgh the UK government has broadly welcomed the document, although it includes an option of giving 16- and 17-year-olds the vote and a separate question on giving Scotland greater powers short of devolution.

The document estimates that the referendum which could herald the greatest constitutional crisis in modern British history will cost about 10 million pounds to stage.

Both proposals are mired in controversy over the role of the UK Electoral Commission in judging whether the questions on independence and potentially extra devolution would be balanced and fair to all sides.

In his first major concession to British Prime Minister David Cameron, the first minister has agreed to allow the commission to run the actual referendum after resisting it for five years.

The concession has come after the UK government offered to make the electoral commission directly answerable to Holyrood. The commission played a key role in the Alternative Vote referendum (on whether to change the voting system used to elect Westminster MP) by rejecting the original wording suggested by Nick Clegg, the deputy prime minister.

Opposition politicians have accused Salmond of trying to rig the referendum.

As Salmond was unveiling the consultation at Holyrood, the Electoral Commission confirmed it would normally expect to assess and validate any referendum question as part of its role, increasing the pressure on the first minister.

At a press conference in Edinburgh Castle later, Salmond admitted to an oversight: “The Electoral Commission will have a role in assessing the questions, can I make that clear. I apologise if the process hasn’t been fully spelt out.”

Salmond has invited representative groups in Scotland to set a second question for the referendum on deeper devolution increasing Holyrood’s powers but keeping Scotland in the UK.

The question would be explored if the groups could ensure the proposals were workable and fund their own campaign.

There were tentative signs of support for this second question on further devolution.

Martin Sime, chief executive of the Scottish Council for Voluntary

Organisations, said: “Politicians ought to step back and give people a chance to think about what the referendum means to them.”

Reform Scotland, a think-tank that has championed “devolution plus”, to allow Holyrood to control about 60% of Scotland’s taxes and its welfare system, said it would submit its proposals for consultation but would not commit to joining a referendum campaign.

Grahame Smith, general secretary of the Scottish TUC, said there were “clear potential difficulties” with setting a devolution question but the issue had to be addressed.

The number of questions is the main obstacle to a deal with Westminster which would ensure the legality of the referendum. Talks were due to begin Thursday but have been postponed after Scottish Secretary Michael Moore came down with chicken pox.