The Scottish parliament has backed First Minister Nicola Sturgeon's bid for a new independence referendum, further complicating Britain's political situation just as years of talks on the terms of Brexit were about to begin.

The UK's vote last year to exit the European Union has strained ties between its four constituent parts because England and Wales voted to leave while Scotland and Northern Ireland voted to remain.

The Edinburgh legislature's vote backing Ms Sturgeon's bid for a referendum in late 2018 or early 2019 came a day before British Prime Minister Theresa May triggers Article 50 of the EU's Lisbon Treaty, the first formal step towards Brexit.

In response, the British government said it would not be entering into negotiations on the Scottish government's proposal to hold a new independence referendum.

"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," it added.

Mrs May had already said "now is not the time" and insisted her focus was on getting a good Brexit deal that would work for every part of the UK.

"Scotland, like the rest of the UK, stands at a crossroads," Ms Sturgeon told the Edinburgh assembly at the start of today’s debate.

"When Article 50 of the Lisbon Treaty is triggered tomorrow, change for our country becomes inevitable ... There will be an impact on trade, on investment and on living standards, and an impact on the very nature of the society we live in."

Scotland voted against independence by 55% to 45% in 2014 but Ms Sturgeon argues circumstances have changed due to the Brexit vote and that Scots should not be dragged out of the EU against their will.

She has proposed a new independence referendum between autumn 2018 and spring 2019, once the terms of Brexit have become clearer but before it has taken effect.

"When the nature of the change that is made inevitable by Brexit becomes clear, that change should not be imposed upon us," she said in parliament.

"The people of Scotland should have the right to choose between Brexit, possibly a very hard Brexit, or becoming an independent country able to chart our own course."

Ms Sturgeon's motion passed by 69 votes to 59.

She has repeatedly said it would be anti-democratic for London to stand in the way of Scotland's elected government if it wanted to hold a referendum.

She said today that if London sought to block her plan, she would return to the Scottish parliament after the Easter break to say how she would handle the situation. She gave no further details.