Theresa May's plan to block a second Scottish independence referendum before a Brexit is "undemocratic and totally unsustainable", Nicola Sturgeon said on Thursday (16 March).

The First Minister of Scotland issued the warning in reaction to May insisting that the UK government would put all of "all its energies" into two-year-long negotiations with the EU.

"As I set out earlier this week, we are not proposing a referendum now - we are proposing to give the people of Scotland a choice once Brexit is clear but before it is too late," Sturgeon said.

"The prime minister does not appear to have listened to our proposal. We will put our proposition, based firmly on this government's democratic mandate, to the Scottish Parliament next week, and then we will put our formal proposals to the UK government.

"If the prime minister refuses to engage on the terms of a referendum before Brexit takes place then she is effectively trying to block the people of Scotland having a choice over their future. That would be a democratic outrage.

She added: "Any bid by the UK government to block the people of Scotland from making a choice will be untenable, undemocratic and totally unsustainable – and clearly shows that the UK government recognises it is out of step with the Scottish people."

Sturgeon ambushed May on Monday when she called for another independence ballot between Autumn 2018 and Spring 2019. But with the Article 50 bill receiving Royal Assent and May set to trigger Brexit talks by the end of March, the Conservative premier rejected Sturgeon's demand.

"I think, just now, we should be putting all our energies into ensuring that we get that right deal for the UK and the right deal for Scotland in our negotiations with the European Union," she told ITV's Robert Peston.

"That is my job as prime minister. Right now, we should be working together, not pulling apart. We should be working together to get that right deal for Scotland, that right deal for the UK. And so, for that reason, I say to the SNP now is not the time."

The move will prove controversial north of the border since David Cameron did grant former First Minister of Scotland Alex Salmond an independence referendum, which saw Scots reject splitting from the rest of the UK in 2014 by 55.3% to 44.7%.

But Scottish voters have since backed Remain at the EU referendum last June by 62% to 38%, with the UK as a whole voting 52% to 48% to leave the bloc. The latest poll from YouGov, of more than 1,000 Scots, found that just 37% backed independence.