Scotland's First Minister Nicola Sturgeon has said she will seek approval next week for a second referendum on Scottish independence.
The SNP leader said the "conditions have been met" to make a formal application for the referendum, arguing Scotland's interests had been ignored by Theresa May's administration ahead of the imminent Brexit negotiations.
The Prime Minister strongly condemned the move, accusing the SNP of "tunnel vision" that sets Scotland "on a course for more uncertainty and division".
She added: "Instead of playing politics with the future of our country the Scottish government should focus on delivering good government and public services for the people of Scotland. Politics is not a game."
In the earlier formal announcement at Edinburgh's Bute House, Ms Sturgeon claimed: "The UK government has not moved even an inch towards compromise.
"The language of partnership has gone."
Labour and the Liberal Democrats also reacted disfavourably to the move, saying they would oppose independence.
Labour leader Jeremy Corbyn claimed there was "no appetite for another referendum" while Lib Dem leader Tim Farron warned: "The SNP are risking taking Scotland out of both the UK and out of the EU. Being outside both would be the worst of all worlds for Scotland."
The Number 10 spokesperson said Scottish public had voted "decisively" in a referendum "which the Scottish Government defined as a 'once in a generation' vote".
A Downing Street spokesman said: "Another referendum would be divisive and cause huge economic uncertainty at the worst possible time."
During her announcement, the first minister said a new independence referendum should be held between autumn 2018 and spring 2019.
She said the justification for a repeat vote, more than two years after 55.3% of Scots chose to remain in the UK, was "beyond doubt".
"The future of the UK looks very different today than it did two years ago," she said.
"We face a future not just away from the EU but from the world's largest single market."
Scots voted 62% to 38% to remain in the EU while the UK as a whole voted to leave.
Ms Sturgeon said she was not "turning (her) back" on future discussions if the UK government agreed to Scotland's compromise proposals.
But she added: "I cannot pretend to the Scottish people that a compromise seems likely."
Ms Sturgeon had called for Scotland to be given a "differentiated deal" which would see it remain part of the European single market through membership of the European Economic Area.
The European Commission has indicated that an independent Scotland would have to apply to join the EU, rather than automatically being a member
On her proposed timing for the second referendum, Ms Sturgeon said: "In my view it is important that Scotland is able to exercise the right to choose our own future at a time when the options are clearer than they are now, but before it is too late to decide our own path."
The first move towards the repeat vote will see Ms Sturgeon ask the Scottish Parliament for permission to request a Section 30 order from Westminster, which is required for a referendum.
Her announcement came as a poll suggested a majority of Scots are against holding another independence referendum before Brexit negotiations are completed.
The BMG survey for The Herald showed about four in 10 Scots support another vote on independence before Brexit happens.
The study suggested the country is split 52-48 in favour of remaining in the Union, adding to findings that support for Scottish independence has increased following the Prime Minister's "hard Brexit" speech in January.