It looks as though a second independence referendum for Scotland is on the horizon, with the First Minister expected to set out plans in her announcement today.

But how will Nicola Sturgeon call on Westminster to give Holyrood the power to do so?

She's expected to seek a Order in Council under Section 30 of the Scotland Act 1998, so that the Scottish Parliament can hold another referendum.

But what does this mean?

What is the Scotland Act 1998?

The Scotland Act 1998 allowed for a Scottish government of ministers and a Scottish Parliament to come into force.

It doesn't specifiy which powers/matters are devolved to the Scottish Parliament, but instead sheds light on those which are reserved to the UK Parliament.

Anything not reserved by the Scotland Act are devolved to the Scottish Parliament.

What does this have to do with independence?

As outlined above, the Act outlines matters which the Scottish Parliament does not have control over - and this includes the 'Union of Scotland and England'.

This means the Scottish Parliament can't actually hold a second referendum without asking for permission to take over this power under the act's terms.

This can be done by changing Schedule 5 through Section 30 of the act.

What is Section 30?

In the Scotland Act 1998, Section 30 reads: “Her majesty may by Order in Council make any modifications of Schedule 4 or 5 which She considers necessary or expedient.”

So really, it grants the opportunity to change Schedule 5 and allow for indyref2.

Has this ever been done before?

Yes - remember that referendum in 2014? That had to go through the exact same process.

Back then, this was the outcome

"On 15 October 2012 the UK and Scottish Governments signed an Agreement on a Referendum on Independence for Scotland. Attached to the Agreement is a draft Order in Council which, under the terms of section 30 of the Scotland Act 1998, will devolve to the Scottish Parliament the competence to legislate for a referendum to be held before the end of 2014 on whether Scotland should become independent of the rest of the United Kingdom."

What does Theresa May say about it?

The Prime Minister doesn't seem to be too happy about Nicola Sturgeon's plans.

UK Government insiders said she thought the issue had been “dealt with” decisively, and said she would reject any push for a fresh vote.

But earlier this month, Nicola Sturgeon said she didn't expect Theresa May would be Prime Minister when the time came to announce a second referendum.

Why now?

It's been in the works for a long time. Nicola Sturgeon asked permission of the Scottish Government back in 2017 because of Brexit, to ask the PM for an agreement to hold another referendum.

It was accepted by 69 votes to 59, and the First Minister then wrote to Mrs May.

She wrote: "The decision of the Scottish Parliament has been made in line with the tradition of popular sovereignty in Scotland - that the people of Scotland should be able to determine the form of government most suited to their needs - and with the clear commitment in the manifesto on which my government was re-elected last May."

Is a second independence referendum in the SNP manifesto?

Yes - the 2016 SNP manifesto is pretty clear in its party's intentions to hold another independence referendum, but only on certain conditions.

They promised to give another vote if there is 'clear and sustained evidence' that independence has become a preferred option of a majority of the Scottish people.

But that's not the only grounds upon which a second vote can be held.

They also said that they'll call for indyref2 if there is a 'significant and material change' in the circumstances of 2014 - specifically, if Scotland is taken out of the EU against its will.

And in light of the 2016 result where 62% of Scottish voted to remain, it seems like that is the case.