Theresa May should not try to block First Minister Nicola Sturgeon’s plans for a second independence referendum, the Scottish National Party has warned.
Deputy leader Angus Robertson said he did not want to “sit in the back of the Tory Brexit bus… and see the prime minister drive us off a Brexit cliff”.
Mr Robertson told BBC Newsnight that the SNP was democratically elected with a mandate to hold a referendum.
The SNP was “playing politics with the future of our country”, said Mrs May.
She also said it was a vote that would only create “more uncertainty and division”.
This was seen as an indication that she would not allow a referendum to go ahead until Brexit negotiations were complete.
Ms Sturgeon announced she wanted a vote to be held between the autumn of 2018 and the spring of the following year.
Mr Robertson said: “I just cannot see how a democratically elected UK government will say to a democratically elected Scottish government which was elected on a mandate to hold a referendum, ‘one’s not going to allow a democratic vote’.”
He added: “We have two options.
“One is to sit in the back of the Tory Brexit bus, shut up, say nothing, and see the prime minister drive us off a Brexit cliff, or we have the opportunity of the people of Scotland having the power in their hands in a referendum about our country’s future.”
Ms Sturgeon’s announcement came as the UK Parliament cleared the way for Mrs May to trigger Article 50 to start the Brexit process.
Peers backed down over the issues of EU residency rights and a meaningful vote on the final Brexit deal after their objections were overturned by MPs.
Sarah Smith, Scotland editor
Nicola Sturgeon may have caught the UK government off guard with her surprise announcement of a second referendum on Scottish independence. But what happens next is not under her control. It is the prime minister who has to power to dictate the timing of another referendum.
Theresa May seems set to refuse another vote before Brexit is completed in two years time. The Scottish first minister insists any referendum must be held before the UK leaves the EU.
Formal negotiations over the timing will not begin until after a vote in the a Scottish Parliament that is scheduled for next Tuesday. The SNP do not have an overall majority in Holyrood but with the support of the Scottish greens they will be able to pass a motion calling for another independence vote.
If Westminster tries to refuse a referendum outright that could well boost support for Scottish independence. But it will make every effort to frustrate Ms Sturgeon’s plans, believing that preparations for a second referendum could undermine the UK’s negotiating position with the rest of the EU.
Ms Sturgeon will ask the Scottish Parliament next Tuesday to request a Section 30 order from Westminster.
The order would be needed to allow a fresh legally binding referendum on independence to be held.
Mrs May has so far avoided saying whether or not she would grant permission.
Responding to Ms Sturgeon’s announcement, Mrs May said a second independence referendum would set Scotland on course for “uncertainty and division” and insisted that the majority of people in Scotland did not want another vote on the issue.
But speaking at her official Bute House residence in Edinburgh, Ms Sturgeon said the people of Scotland must be offered a choice between a “hard Brexit” and becoming an independent country.
The Scottish government has published proposals which it says would allow Scotland to remain a member of the European single market even if the rest of the UK leaves, which Mrs May has said it will.
The first minister said the UK government had not “moved even an inch in pursuit of compromise and agreement” since the Brexit referendum, which saw Scotland vote by 62% to 38% in favour of Remain while the UK as a whole voted to leave by 52% to 48%.
Ms Sturgeon will rely on the pro-independence Scottish Greens to give her plans majority support in the Scottish Parliament.
Patrick Harvie, the party’s co-convener, welcomed the announcement and confirmed the Greens would vote in favour of seeking a Section 30 order.
Scottish Conservative leader Ruth Davidson said Ms Sturgeon had been “utterly irresponsible” and had “given up acting as first minister for all of Scotland”.
She added people “do not want to go back to the division” of a referendum and that Ms Sturgeon had promised the 2014 referendum would be a “once in a generation” poll.
Scottish Labour leader Kezia Dugdale said Scotland was “already divided enough” and “we do not want to be divided again, but that is exactly what another independence referendum would do.”
But the party’s UK leader, Jeremy Corbyn, confirmed that his MPs would not attempt to block a request for a Section 30 order.
Scottish Liberal Democrat leader Willie Rennie said Ms Sturgeon’s SNP had been “working towards this announcement for months” and were “determined to contrive a way to ignore their promise that 2014 was ‘once in a generation’.”