NICOLA Sturgeon has told the Prime Minister there is “no rational reason” for her to block an independence referendum.

The message was included in the letter the First Minister wrote to Theresa May with a formal request for a Section 30 order, the mechanism to transfer the powers to Holyrood to hold a plebiscite.

MSPs voted by 69 to 59 this week in favour of holding an independence referendum to take place between autumn 2018 and spring 2019 – a timescale in which it is expected the terms of the UK’s departure from the EU are known but before the actual date of departure.

The UK Government has said it will decline the request, with May repeatedly stating “now is not the time” for another vote on the issue.

In a letter sent by email and courier to Downing Street, Sturgeon told the Prime Minister: “There appears to be no rational reason for you to stand in the way of the will of the Scottish Parliament and I hope you will not do so.

“However, in anticipation of your refusal to enter into discussions at this stage, it is important for me to be clear about my position.

“It is my firm view that the mandate of the Scottish Parliament must be respected and progressed. The question is not if, but how.”

About 62 per cent of Scottish voters backed Remain in the EU referendum and the SNP’s manifesto for last year’s Holyrood elections said another ballot on independence should take place if there were a ‘’material change in circumstances’’ from the previous ballot in 2014, such as Scotland being removed from the EU against its wishes.

“In these very changed circumstances, the people of Scotland must have the right to choose our own future – in short, to exercise our right of self-determination,” the First Minister told May in her letter.

In a video message posted by the Scottish Government on Twitter, Sturgeon added: “The Prime Minister has indicated that she intends to ignore the will of the Scottish Parliament and seek to prevent people in Scotland having that choice.

“If the Westminster government continues to hold that line, it will go against the very foundations of devolution.

“So, I hope the Prime Minister changes her mind and acknowledges that the people of Scotland are entitled to a choice at a time and in a way that is right for Scotland.

“However, if she doesn’t, as I expect she won’t, at least not yet, I will come back to the Scottish Parliament in a few weeks’ time with an update on how we’re going to move forward to ensure that the people of Scotland are able to choose our future when we have the information we need both about Brexit and about independence, and while there is still time to take a different path.”

Downing Street confirmed that the letter was received by email and a response would be sent in due course.

A UK Government spokeswoman said: “The Prime Minister has been clear that now is not the time for a second independence referendum and we will not be entering into negotiations on the Scottish Government’s proposal.

“At this point, all our focus should be on our negotiations with the European Union, making sure we get the right deal for the whole of the UK.

“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.

“We have been joined together as one country for more than 300 years. We’ve worked together, we’ve prospered together, we’ve fought wars together and we have a bright future.

“At this crucial time we should be working together, not pulling apart.”

Scottish Conservative, Labour and Liberal Democrat politicians oppose another referendum insisting Scots “do not want one”.

However, a Panelbase poll, carried out between 13 and 17 March, found that 50 per cent of voters believed there should be a new independence referendum either during the UK/EU Brexit negotiations (32 per cent), or “in about two years” once those talks were completed (18 per cent).

The same poll also revealed that only 26 per cent of voters did not believe Scotland was likely to become independent.

Jackson Carlaw, the Scottish Conservative deputy leader, said the First Minister’s plans were “unwanted” and “unworkable.”

“She wants a referendum campaign to start right now – despite still not having answered basic questions on the currency, on EU membership and the cost of independence,” he said.

“Nicola Sturgeon should dump her referendum plans now, work to get the best deal possible Brexit deal for Scotland and the UK – and then get back to the day job of improving our schools and hospitals, as she promised.”

Scottish Labour leader Kezia Dugdale said: “Scotland doesn’t need or want a second independence referendum. There is absolutely no evidence that another divisive referendum is the will of the people of Scotland. We need the SNP government to get on with the job of governing.”

Scottish Liberal Democrat leader Willie Rennie MSP said: “I proudly voted remain in June but I did not vote remain so that the First Minister could continue with her obsession on independence.”