The SNP has warned Theresa May not to slam the brakes on a second independence referendum amid a growing belief the Prime Minister will try to delay it until after Brexit.

Ms May has been careful not to reject a fresh referendum, a move which would be likely to rouse support for independence. But ministers fear having the poll during EU exit negotiations would undermine the UK's position.

However, deputy leader Angus Robertson insisted the SNP was right to press for the vote as early as autumn next year – rather than “see the prime minister drive us off a Brexit cliff".

“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',” Mr Robertson told BBC Newsnight.

“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 May will be under pressure to reveal her stance on an early second referendum – which Westminster has the power to block – when she delivers a statement on last week’s EU summit later today.

However, Number 10 has signalled she will not state her position until after the Scottish Parliament has voted for the referendum, probably next Tuesday.

One Government source told The Times that the Prime Minister would not allow a referendum during the perilous exit negotiations with the EU.

“The prime minister has said this would mean a vote while she was negotiating Brexit and I think that can be taken pretty clearly as a message that this timing is completely unacceptable. It would be irresponsible to agree to it and we won't,” the source said.

Last night MPs and Lords passed the Article 50 bill, giving Ms May the power to trigger Brexit – but her victory was overshadowed by Ms Sturgeon's shock demand for a plebiscite hours before.

Although the SNP First Minister successfully ambushed Number 10 with the move, what happens next is out of her hands.

The Government will also undoubtedly come under huge pressure from its MPs and Brexit-backing papers not to allow preparations for a second referendum to undermine the negotiations.

Formal negotiations over the timing will not begin until after next week’s vote at Holyrood, when the Scottish Greens will give the SNP the majority it needs to approve another independence vote.

Meanwhile, Fiona Hyslop, the SNP’s culture minister, denied that an independent Scotland would necessarily be forced to adopt the euro.

She insisted it would depend on whether independence came before or after Brexit, telling the BBC Radio Four’s Today programme: “You are pre-empting the position we may find ourselves in.”

However, the EU has restated its position that Scotland would be treated as a new member, if it applied to join – and new members are required to use the single currency.