Scotland's first minister formally requested a second referendum on independence on Friday, declaring that Scots have the right to exercise their right of self-determination.

Nicola Sturgeon sent U.K. Prime Minister Theresa May a letter formally requesting the transfer of powers to allow a second vote. Sturgeon argued that Britain's planned exit from the European Union's single market is an outcome that will have significant implications on Scotland, which voted in favor of remaining in the EU.

"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," Sturgeon wrote.

The letter followed a 69-59 vote in the Scottish Parliament this week in favor of asking for an independence referendum. The Scots want the vote to take place between autumn 2018 and spring 2019.

Britain's government has said it will deny the request. May has made clear she does not believe it is the time for another vote. Scottish voters rejected independence in a 2014 referendum that Sturgeon's Scottish National Party called a once-in-a-generation vote. But Sturgeon says Brexit has altered conditions dramatically.

May's Downing Street office confirmed that the letter had been received. It said it would respond in due course.

Sturgeon said there appeared to be "no rational reason" to deny a vote.

"It is my firm view that the mandate of the Scottish Parliament must be respected and progressed," she wrote. "The question is not if, but how."

"I hope that will be by constructive discussion between our governments." Sturgeon continued. "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."

Some 62 percent of Scottish voters were in favor of remaining in the EU in last June's plebiscite.(ABC)