NICOLA Sturgeon will not produce any legislation today to back up her plan to hold a second referendum, the Herald understands.

The First Minister is due to set out her “route map” to independence to MSPs this afternoon with an eye to holding a vote in October 2023.

However the Scottish Parliament has not received an Indyref2 Bill from the Scottish Government in time for an introduction today.

It is understood there is also unlikely to be an Indyref2 Bill introduced by summer recess, which starts at the end of this week.

A Scottish Government source revealed no Bill had been sent to Holyrood as of last Thursday, leaving it too late to complete the three-week "pre-introduction period" required by the parliament.

That means the earliest opportunity for bringing forward legislation will be when the Scottish Parliament returns in September.

The development will potentially disappoint Yes movement supporters, who were promised a "substantial update" today by the SNP leader.

In the run up to the independence referendum of September 2014, the Scottish Government introduced a Referendum Bill in March 2013, almost 18 months before the vote.

However that referendum was based on an agreement between the Scottish and UK governments and the transfer of powers to stage the vote via a so-called Section 30 order.

Ms Sturgeon asked Boris Johnson for a fresh Section 30 order after the 2019 general election, but he refused in early January 2020, saying the No result of 2014 was a “once in a generation event” and he would not transfer any powers leading to Indyref2.

Earlier this month, Ms Sturgeon published the first instalment of a new prospectus for independence, but refused to discuss the timing of legislation on which to hold it.

She admitted she may have to proceed in the absence of a Section 30 order, something she has previously resisted, warning it could be a backward step.

The issue of whether Holyrood can hold a referendum on independence using devolved powers has never been determined by the UK Supreme Court.

As the Union is an issue reserved to Westminster, it appears any unilateral referendum  on the issue would struggle, either because the Lord Advocate would not allow ultra vires legislation to go forward in the first place, or because the UK Government would challenge any legislation that Holyroood did pass on the grounds it was legislatively incompetent.

There is speculation at Holyrood that Ms Sturgeon might try to avoid a court case by holding a democratic event short of a full-blown referendum to consult the people on independence.

However the UK Government could refuse to recognise it, invalidating it in the eyes of the international community as well.

Unionist parties could also boycott it in an attempt to deny it legitimacy.

The Times today reported that the Scottish Government has already told a handful of foreign diplomats to expect referendum legislation in the autumn, after summer recess.

The Scottish Government has repeatedly refused to say if an Indyref2 Bill will be introduced at Holyrood today.