A letter from Nicola Sturgeon formally requesting transfer of powers to hold a second Scottish independence referendum has been delivered to Downing Street.
The Section 30 letter penned by Scotland's First Minister was dispatched to Prime Minister Theresa May on Friday morning.
MSPs voted by 69 to 59 this week in favour of seeking permission for an independence referendum to take place between autumn 2018 and spring 2019.
The letter said: "In these very changed circumstances, the people of Scotland must have the right to choose our own future - in short, to exercise our right of self determination."
The UK Government has said it will decline the request, with Mrs May repeatedly stating "now is not the time" for another vote on the issue.
However, Ms Sturgeon has said her mandate for another vote is ''beyond question'' and is pressing ahead with a formal approach for a Section 30 order - the mechanism for the powers to hold a referendum.
Ms Sturgeon said leaving the EU and the single market would have "enormous implications" for schools, hospitals, jobs and investment in Scotland.
In a video message posted by the Scottish Government on Twitter, she said: "The next two years are hugely important for Scotland because they will determine the kind of country we'll become.
"That's why I have today written to the UK Government to ensure that we can make that choice when the time is right to accept Brexit or instead become an independent country.
"I don't take for granted how people would vote when that choice comes but I hope we can all agree that the future of our country is our choice."
She added: "The Prime Minister has indicated that she intends to ignore the will of the Scottish Parliament and seek to prevent people in Scotland having that choice.
"If the Westminster government continues to hold that line, it will go against the very foundations of devolution.
"So, I hope the Prime Minister changes her mind and acknowledges that the people of Scotland are entitled to a choice at a time and in a way that is right for Scotland.
"However, if she doesn't, as I expect she won't, at least not yet, I will come back to the Scottish Parliament in a few weeks' time with an update on how we're going to move forward to ensure that the people of Scotland are able to choose our future when we have the information we need both about Brexit and about independence, and while there is still time to take a different path."
In the letter to Mrs May, Ms Sturgeon said there appeared to be "no rational reason" for the UK Government to "stand in the way of the will of the Scottish Parliament", adding: "I hope you will not do so."
She continued: "However, in anticipation of your refusal to enter into discussions at this stage, it is important for me to be clear about my position.
"It is my firm view that the mandate of the Scottish Parliament must be respected and progressed. The question is not if, but how.
"I hope that will be by constructive discussion between our Governments. However, if that is not yet possible, I will set out to the Scottish Parliament the steps I intend to take to ensure that progress is made towards a referendum."
Around 62% of Scottish voters backed the UK remaining part of the EU in June 2016 and the SNP manifesto for last year's Holyrood elections said another ballot on independence should take place if there were a ''material change in circumstances'' from the previous ballot in 2014.
The example cited was for Scotland to be removed from the EU against its wishes.
Scottish Conservative, Labour and Liberal Democrat politicians oppose another referendum.
A UK Government spokeswoman said: "The Prime Minister has been clear that now is not the time for a second independence referendum, and we will not be entering into negotiations on the Scottish Government's proposal.
"At this point, all our focus should be on our negotiations with the European Union, making sure we get the right deal for the whole of the UK.
"It would be unfair to the people of Scotland to ask them to make a crucial decision without the necessary information about our future relationship with Europe, or what an independent Scotland would look like.
"We have been joined together as one country for more than 300 years. We've worked together, we've prospered together, we've fought wars together, and we have a bright future. At this crucial time we should be working together, not pulling apart."
Downing Street confirmed that the letter was received by email and a response would be sent in due course.
Scottish Labour leader Kezia Dugdale said: "People across Scotland will be dismayed that Nicola Sturgeon is more focused on re-running the arguments of the past than doing her job of running our public services.
"Scotland doesn't need or want a second independence referendum.There is absolutely no evidence that another divisive referendum is the will of the people of Scotland.
"We need the SNP Government to get on with the job of governing."