NICOLA Sturgeon’s office insisted there would be a second referendum in the current Scottish Parliament, but accepted it might not be until May 2021.

Setting out her preferred timetable on Monday, the First Minister said she wanted Scots to choose between Brexit in the UK or independence between autumn 2018 and spring 2019.

However she was careful to leave some wriggle room, saying the vote should be before Brexit “or at least within a short time after it”.

She repeated the point the next day, saying the choice should be “when the terms of Brexit are clear but before the UK leaves the European Union or shortly afterwards”.

At a media briefing after Theresa May’s statement, the First Minister’s official spokesman was asked the cut-off date for a possible second referendum.

He said: “The mandate is clear. The mandate is for this parliamentary term.”

Asked if that meant the SNP government therefore wanted the referendum “at some point before May 2021”, the date of the next scheduled Holyrood election, he said: “Yes.”

Asked if the government could accept a referendum up to 2021, he said: “The First Minister has made clear her preferred timescale and that is the timescale we are working to.

“But the mandate is for this parliament. The basis on which this government was elected is the mandate in the manifesto, the manifesto covers the parliamentary term.”

The elastic timetable suggests Ms Sturgeon had already calculated the UK Government might try to delay a referendum beyond Brexit, and could accept that.

However with her mandate expiring in 2021 and no guarantee of a pro-independence majority in the next Scottish Parliament, she will also insist on cashing it in this term.

“There’s going to be an independence referendum,” her spokesman said.

He added: “This issue is not going away. There is an absolutely rock solid, crystal clear mandate for this referendum to happen.

He also said that blocking a referendum would “play disastrously” with Scottish voters, and prove to be a “miscalculation of epic and historic proportions”.