The UK government is to reject calls for a Scottish independence referendum before Brexit after Theresa May said “now is not the time”.
The prime minister said the focus should be on getting the best Brexit deal for the whole of the UK.
Scottish Conservative leader Ruth Davidson said Nicola Sturgeon’s demand for a vote by the spring of 2019 would be rejected “conclusively”.
Ms Sturgeon said blocking a referendum would be a “democratic outrage”.
Ms Sturgeon, the Scottish first minister, told BBC Scotland: “It is an argument for independence really in a nutshell, that Westminster thinks it has got the right to block the democratically elected mandate of the Scottish government and the majority in the Scottish Parliament.
“You know history may look back on today and see it as the day the fate of the union was sealed.”
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Ms Sturgeon has called for a referendum to be held in the autumn of 2018 or the spring of the following year, to coincide with the conclusion of the UK’s Brexit negotiations with the EU.
But Mrs May said her message to Ms Sturgeon was clear – “now is not the time”.
The prime minister added: “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 the people of Scotland that they would be being asked to make a crucial decision without the information they need to make that decision.”
The prime minister also said the country should be “working together, not pulling apart”.
The prime minister was speaking as Nicola Sturgeon took part in first minister’s questions at Holyrood
Media captionRuth Davidson says a second Scottish independence referendum should only be held after the UK leaves the EU
Ms Davidson later told a media conference in Edinburgh that the people of Scotland should have the right to see how the UK was working after leaving the EU before deciding whether or not they wanted independence.
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She added: “People should only be asked to make a judgment on whether to leave or remain within a 300-year-old union of nations when they have seen for themselves how that union is functioning following Brexit.
“They should also know what the alternative entails and we have seen no clarity from the SNP on even the basic questions of their proposition.”
Analysis by Norman Smith, BBC assistant political editor
What we heard from Theresa May was a very carefully calibrated rebuff to Nicola Sturgeon – but not to the Scottish people.
You sense that Mrs May is trying to drive a wedge between the two. She’s rejected the first minister’s call for a referendum before Brexit, saying all our energies now need to be focused on getting the best deal.
But the prime minister is absolutely not ruling out a referendum in the future.
Now may not be the time – but she’s not saying never.
Scotland voted by 55% to 45% to remain in the UK in a referendum in September 2014 – but Ms Sturgeon says a second vote is needed to allow the country to choose what path to take following last year’s Brexit vote.
MSPs are due to vote next Wednesday on whether to seek a section 30 order from the UK government, which would be needed to make any referendum legally binding.
The parliament currently has a pro-independence majority, with the Scottish Greens pledging to support the minority SNP government in the vote.