UK Edition Theresa May has formally rejected Nicola Sturgeon’s timetable for a second independence referendum, saying "now is not the time".
The Prime Minister ruled out Ms Sturgeon's demand for another vote between autumn 2018 and spring 2019, saying that it would be "unfair" on Scots to vote then as it would be too early to pass judgement on Brexit. However, she did not rule out a second referendum indefinitely.
She accused the SNP of jeopardising the UK's negotiations with the EU with talk of a second referendum and said "working together" was the best chance for Scotland and for the rest of the UK to get the best deal in the wake of the Brexit vote.
Mrs May told ITV News: "My message is very clear - now is not the time. I've explained the reasons why. I think we should be working to get the right deal for Scotland and the UK with our future partnership with the European Union.
"It would be unfair to Scotland, the people of Scotland at the moment that they would be being asked to make a crucial decision without the information they need to make that decision."
The Prime Minister added: "Just at this point, all our energies should be focused on our negotiations with the European Union about our future relationship. To be talking about an independence referendum will make it more difficult for us to be able to get the right deal for Scotland, and the right deal for the UK.
"And more than that, I think it wouldn't be fair to the people of Scotland because they're being asked to make a crucial decision without all the necessary information - without knowing what the future partnership would be, or what the alternative of an independent Scotland would look like."
Mrs May also said: This Union we have is very precious. We've been joined together for over 300 years. We've had a great history together - I believe we have a great future together.
"Together, we should put our energies into making sure we get the right deal for Scotland and for the whole of the UK."
Nicola Sturgeon responds on Twitter
Mrs May’s decision will not be impacted by the outcome of a vote at the Scottish Parliament next Wednesday on giving Ms Sturgeon authorisation to ask the Prime Minister for the power to stage another referendum.
The powers would be transferred using a legal mechanism called a Section 30 order.
Her rejection is expected to prompt a furious reaction from Ms Sturgeon, who argued that Holyrood - which has a nationalist majority when SNP and Green MSPs are combined - must have control over the referendum's timing.
However, the arrangements for the 2014 vote were the result of a consensus deal reached by both the UK governments. Although Alex Salmond was given the power to set the specific date, David Cameron set a cut-off point of the end of 2014.
Ruth Davidson, the Scottish Tory leader, and David Mundell, the Scottish Secretary, are also holding a press conference in Edinburgh on Thursday afternoon.
Speaking after First Minister's Questions at Holyrood, Ms Davidson said: "“The Scottish Conservatives reject the proposals set out by the First Minister on Monday. A referendum cannot happen when the people of Scotland have not been given the opportunity to see how our new relationship with the European Union is working.
“And it should not take place when there is no clear political or public consent for it to happen. “Our country does not want to go back to the divisions and uncertainty of the last few years. Another referendum campaign will not solve the challenges this country will face. We don’t want it. We don’t need it.”
But Ms Sturgeon said: "If the Prime Minister refuses to engage on the terms of a referendum before Brexit takes place then she is effectively trying to block the people of Scotland having a choice over their future. That would be a democratic outrage.
“It is for the Scottish Parliament – not Downing Street – to determine the timing of a referendum, and the decision of the Scottish Parliament must be respected. It would be outrageous for the Scottish Parliament to be frozen out of the process.
“The Scottish Government has a cast-iron democratic mandate to offer people a choice and that mandate must be fulfilled.
“Any bid by the UK Government to block the people of Scotland from making a choice will be untenable, undemocratic and totally unsustainable – and clearly shows that the UK Government recognises it is out of step with the Scottish people.”
In her press conference on Monday, Ms Sturgeon said that autumn next year would be the earliest "appropriate" time as only then will the shape of the Brexit deal be known, but also that a second independence referendum could not be held long after the UK leaves the EU in March 2019.
She argued that staging another referendum much later than spring 2019 would deny Scotland the chance to indicate to the EU that it wants a “different relationship” than leaving with the rest of the UK.
The First Minister said that a later date for a referendum could mean Scotland being left outside the EU and single market for a “lengthy period”, making the task of getting membership “much more difficult.”
Mrs May’s announcement, on the eve of the SNP conference in Aberdeen, follows a series of opinion polls showing a majority of Scots do not want another referendum before Brexit in March 2019.