THERESA May has set herself on a constitutional collision course with the Scottish Government after she signalled she would reject a request for Holyrood to hold an independence referendum before Brexit.

Nicola Sturgeon described the Prime Minister’s stance as a “democratic outrage” as a war of words broke out between Edinburgh and London over the right of the Scottish people to a new vote.

In an sign of the deterioration of relations between the two governments, the Prime Minister indicated she would any request for the legal mechanism to hold a referendum during the timetable desired by the First Minister in a television interview while the Sturgeon was in the Holyrood debating chamber for First Minister’s Questions.

It came as the Scottish Government prepare to ask the Scottish Parliament next week to vote on a request for a section 30 order. The mechanism is needed so that Holyrood can hold a legally binding ballot and as a majority of MSPs support independence there is no doubt the vote will go through.

Responding to May’s veto, the First Minister said: “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.

“It is for the Scottish Parliament —not Downing Street — to determine the timing of a referendum, and the decision of the Scottish Parliament must be respected.

“It would be outrageous for the Scottish Parliament to be frozen out of the process. The Scottish Government has a cast-iron democratic mandate to offer people a choice and that mandate must be fulfilled.”

In a interview with BBC Scotland, Sturgeon added: “This is like winding the clock back to the bad old days of Margaret Thatcher. It is an argument for independence really in a nutshell, that Westminster thinks it has got the democratically elected mandate of the Scottish Government and the majority in the Scottish Parliament.

“History may look back on today and see it as the day the fate of the Union was sealed.”

Sturgeon wants a referendum to take place between Autumn 2018, when the terms of the UK’s departure are due to be ratified and the Spring 2019, when the UK is due to leave the bloc. She believes by having it before Brexit it would be easier to protect Scotland’s links with the EU than if the country comes out of the bloc along with the rest of the UK.

But May has insisted Scotland will have to leave with the rest of the UK.

‘’Right now we should be working together, not pulling apart,” May told ITV News.

‘’We should be working together to get that right deal for Scotland, that right deal for the UK, as I say that’s my job as Prime Minister and so for that reason I say to the SNP: now is not the time.”

She added that to be “talking about an independence referendum will, I think, make it more difficult for us to be able to get the right deal for Scotland, and the right deal for the UK”.

She said: ‘’More than that I think it wouldn’t be fair to the people of Scotland because they’d be asked to make a crucial decision without the necessary information, without knowing what the future partnership will be or what the alternative for an independent Scotland would look like.”

Ross Greer, external affairs spokesperson for the Scottish Greens, responded angrily to May’s intervention. “Scotland deserves to choose between the isolated, angry Brexit Britain planned by the Tories and putting our future in our own hands with independence,” he said.

“If a Tory Westminster Government that Scotland did not elect seriously think they can block our right to choose — and that they can veto a decision of our elected parliament – they will only increase support for independence. Today’s comments underline the contemptuous attitude the Tories have toward Scotland.”

He added: “It is quite clear that the Brexit deal will be known by autumn 2018, following comments from Europe’s lead negotiators. For a government dragging Scotland through a hard Brexit without a mandate and after an EU referendum where no details were presented it reeks of hypocrisy to say we have to wait. This seems like a transparent attempt to deny ...the Scottish people as a whole, a vote on our collective future at the critical moment.”

But the Unionists parties fell into line behind May with both Scottish Labour leader Kezia Dugdale and Scottish Lib Dems leader Willie Rennie said they were opposed to a second independence referendum.