Nicola Sturgeon has issued a direct challenge to Theresa May, pointing out that she was voted in on a clear manifesto commitment to Scottish independence but that the Prime Minister “is not yet elected by anyone”.

In a taunting reminder that Ms May’s premiership is yet to be endorsed by the public at a general election – or even by all members of her own party – the Scottish First Minister said she had the mandate to call a second referendum on independence.

Ms Sturgeon pointed out that she had been elected as First Minister with a greater share of the vote than the Conservative Party secured at the 2015 general election. “Trading mandates does not put the PM on strong ground,” she added.

Second Scottish Independence Referendum to be held, announces Sturgeon

“A quick reminder: Tory vote in GE2015 – 36.9%, SNP constituency vote in SP2016 – 46.5%,” she wrote on Twitter.

“In addition, I was elected as FM on a clear manifesto commitment re #scotref. The PM is not yet elected by anyone,” the First Minister said.

It comes after one Government source told The Times that Ms May 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 impossible to agree to it and we won’t,” the source added.

Announcing her intention to trigger the poll on Monday, Ms Sturgeon said the Westminster government had “not moved even inch in pursuit of compromise and agreement” with Holyrood over Brexit and even a good deal would be “significantly inferior” to the status quo.

Her statement came after Spain suggested Scotland would be at the “back of the queue” to join the EU if it achieves independence.

The First Minister said the vote had to be held between Autumn 2018 and Spring 2019 – before it was “too late” but after “the terms of Brexit are known”.

However, the Westminster parliament must authorise any such poll – meaning Ms Sturgeon’s call could be blocked by Ms May, who attacked the move, accusing her Scottish counterpart of playing “games” and the SNP of having “tunnel vision”.