THE Prime Minister cannot keep dismissing requests from the Scottish Government for a second independence referendum.

That’s according to leading experts who have calculated the process to hold a new vote could take place just 15 weeks after Westminster and Holyrood approve its terms.

The London-based Institute for Government said the UK should accept Scotland has the right to become independent if Scots vote for parties which support a fresh plebiscite. It added it would be “unsustainable” for a new vote to be denied under such circumstances.

“Devolution in 1999 was founded on the principle that it is the sovereign right of the Scottish people to determine the form of government best suited to their needs,” said the IFG report.

“In 1997 and again in 2014, the Scottish people decided that devolution is the form of government that best suited their needs. Should they decide at some future date that independence is now the answer, then that should ultimately be respected.”

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The report added: “If the Scottish people choose to vote for political parties that favour a referendum, then a blanket refusal will not be sustainable.

“If the Union is to survive, it must be because a majority of people in all four parts of the UK are persuaded that its survival is for the best, not because Westminster wields the power of parliamentary sovereignty to hold the nations of the UK together against their will.”

The study also found a No-Deal Brexit is likely to increase support for independence and said a referendum could be held within 15 weeks once the Section 30 order legislation had passed through both parliaments. This is due to provisions made in the Referendums (Scotland) Bill currently going through Holyrood.

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“No Deal is likely to increase support for a second independence referendum and the terms of the Referendums (Scotland) Bill mean that if and when the power to hold one is devolved, the Scottish Government would be able to do so held on an expedited timetable,” the report said.

“The Bill ... allows ministers to provide for a referendum by regulation, removing the need for primary legislation.

“The Bill also provides an exemption from Electoral Commission question testing – which usually takes 12 weeks – for referendum questions that have been tested before. Therefore, if the 2014 referendum question were used again, the legal basis for the vote could be approved within just eight weeks.

It continued: “The Bill also allows Scottish ministers to specify the length of the referendum period during which the campaign rules apply. There is no minimum specified in the Bill, so it could be as short as one week.

“Before this campaign period starts there must be a six-week period during which lead campaigners for each outcome are designated, but the time between approval of the legislation and polling day could be as little as seven weeks.

“This means that in total, a minimum timetable for the whole referendum process is 15 weeks.”

However, the IFG report added “important constitutional decisions must not be rushed ... to ensure that the referendum result commands widespread legitimacy, there must be full scrutiny of the basis for the referendum and time for citizens to deliberate on the issues”.

The IFG has previously recommended changes to the Referendums Bill, including removing the question-testing exemption.

At the SNP conference on Tuesday, Nicola Sturgeon restated her intention to hold a referendum next year and would demand the powers to hold it by the end of this year.

In July, Boris Johnson declared there was “no reason” for a second independence referendum and that people had been assured it was a “once in a generation event” in 2014.

Last month, the Prime Minister repeated that declaration: “They [Scots] were promised this was a once-in-a-generation thing and I think we should stick with that.”

Labour leader Jeremy Corbyn has indicated he would “not rule out” consent for a second referendum, although it would be not be authorised by his government in its “formative years”.