By Michael Settle, Kate Devlin & Tom Gordon

DAVID Mundell has given the clearest signal yet that Theresa May will refuse to facilitate a second independence referendum before a Brexit deal is done, warning that Nicola Sturgeon’s desired timeframe means a second poll would not be “legal, fair and decisive” as the 2014 vote was.

And the Scottish Secretary, in an exclusive interview with The Herald, made clear that Scotland would be leaving the European Union alongside the rest of the UK, dismissing as “absurd” the notion that another independence poll could prevent this.

Mr Mundell’s remarks came as the First Minister warned Whitehall that there should be "no blocking mechanisms" applied to her plans for a second independence poll.

She also made clear that another referendum should be “made in Scotland” with Holyrood not Westminster determining its timing, franchise and question.

And in a direct attack on the Prime Minister, Ms Sturgeon suggested trading mandates did not put Mrs May on strong ground, tweeting: “I was elected as FM on a clear manifesto commitment re #scotref. The PM is not yet elected by anyone."

Meantime today, the annual Scottish Social Attitudes survey will give the SNP leadership a lift, saying that independence has become the most popular constitutional choice for the first time, backed by 46 per cent of people, compared to 42 per cent favouring devolution. In 2012, support for independence was just 23 per cent.

However, the study also found Euroscepticism among Scots, especially Unionists, was on the rise, potentially making it harder for Ms Sturgeon to win converts to independence if the EU remained central to the SNP’s campaign.

At Holyrood, it emerged that her bid to seek a mandate from the Scottish Parliament to call for another referendum on Scotland’s future will be voted on by MSPs next Wednesday.

Whitehall sources refused to say when the PM would formally respond to the FM’s referendum demand but stressed: “It will be at a time of our choosing.” It could come in the next week or two.

At Westminster, Downing Street continued to deflect questions about when Mrs May would deliver her formal response to Ms Sturgeon’s referendum demand, repeating only the line that there should not be another vote.

Last month, Sir Michael Fallon, the Defence Secretary, when asked if the UK Government would facilitate a second poll in this parliament by granting Holyrood a Section 30 parliamentary order, declared: “No, forget it.”

In his interview, the Scottish Secretary suggested that it would be unfair to people to offer them a vote on the future of Scotland, based on Brexit, when Ms Sturgeon’s timeframe – autumn 2018 to spring 2019 - would mean they would not be aware of the full details of the UK deal on EU withdrawal.

"It would be impossible for people in the timescale suggested by Nicola Sturgeon to make a reasoned view and, therefore, have a legal, fair and decisive referendum as we did in 2014 on the basis of the facts as they would be aware of them at that point.

“If you are saying you want the referendum because of Brexit, then you have to know what the arrangement is that the UK has secured in relation to leaving the EU and how that has been delivered and, of course, you need to know what the SNP alternative to that proposal is," he explained.

In the Commons, the PM again rebuked Ms Sturgeon, telling MPs: “This is not a moment to play politics or create uncertainty and division; it is a moment to bring our country together.”

She warned for the first time that the Brexit talks could go down to the wire, ie March 2019, delivering another blow to Ms Sturgeon’s timeframe. She told MPs: “We have a timetable of up to two years for the negotiations and it is possible the details will not be finalised until close to the end of that period.”

Mr Mundell explained how another independence poll would go against the wishes of the Scottish public, a majority of whom, opinion polls suggested, were opposed to holding another poll. He also claimed businesses were “absolutely dismayed” at the prospect of the uncertainty and instability another referendum would bring.

He said that it had been “inevitable for some time” that the FM would make her referendum demand but noted how the UK Government would issue its full response “at the appropriate time”.

On the issue of an independent Scotland remaining in the EU, the Secretary of State declared: “There is no option for Scotland to remain in the EU as the UK leaves or for Scotland to inherit the UK’s place. There’s an implicit suggestion in the timing of the referendum demand that somehow by having a referendum and by voting for independence you can stop Scotland leaving the EU; that’s absurd.

“Scotland will leave the EU. An independent Scotland would be required to apply to join the EU,” he added.

In a separate development, Alfonso Dastis, the Spanish Foreign Minister, made clear an independent Scotland would be "at the back of the queue" if it wanted to become a member of the Brussels bloc.

Travelling in Peru, he told reporters an independent Scotland "can't just stay in the EU".