But, in summary, the decision of Theresa May to call an early UK General Election means that the next Holyrood Election will be in May 2020 rather than May 2021 as would otherwise be the case.
The Scottish Parliament was meant to have a four year term and in 1999, 2003, 2007 and 2011 that's what happened.
But in 2011, the Westminster Parliament passed the Fixed-Term Parliaments Act essentially fixing the date of the Next UK General Election for May 2015. That would however have meant a Holyrood poll on the same date and, for reasons I don't have time to go into here, there was a consensus against that. So, by virtue of s.4 of the 2011 Act, the date of the next Holyrood poll was moved to May 2016.
This was done on a one-off basis originally but there remained a view that the two elections should not clash, so when the Scotland Act 2016 was introduced it contained (in ss.4-10) provision that if a Holyrood and Westminster poll was to clash in future, the former would be moved.
The power to actually change the date lies with the Secretary of State but undertakings were given that he would respect the preference of the Scottish Government on whether to move the poll backwards or forwards. Prior to May 2016, Nicola Sturgeon indicated her preference for the former option.
BUT, although ss 4-10 of the 2016 Act were passed they have not been commenced. Even if they were commenced however, the power to adjust the four year statutory term would only be available if there was going to be a clash, which patently there isn't now going to be.
So its May 2020 for the next Holyrood poll.
Now, this is very important.
It has been clear from the outset that Sturgeon wanted the "next" referendum before the next Scottish Parliament election. The reason for that is quite clear. She fears the Parliament's pro independence majority might be lost at that poll. But, while suggesting her own preference for Autumn 2019, she was realistic enough to concede that it might have has to have been May 2020 for reasons connected to the negotiation of the terms of a s.30 and the inevitable time it would take to get a Bill through the Scottish Parliament.
Well it can't be May 2020 now. And the Tories have made it clear it won't be Autumn 2019.
So, there will only now be a second referendum if the SNP (and any allies) win the May 2020 elections on a clear mandate for a second vote. A mandate they fear they won't get. Don't take my word for that, ask Nicola Sturgeon.
Since I wrote this hurriedly at lunchtime, Professor James Chalmers of the University of Glasgow has entered this debate to suggest I am wrong and the Scottish Parliament has also claimed that the May 2021 date is preserved. I haven't seen anything in writing from the latter but am relying on what I've been told by political journalists who suggest they are following Professor Chalmers logic, so I'll assume that to be the case.
I accept absolutely that the Prof's only dog in this fight is that of correct statutory interpretation and that he is undoubtedly a more distinguished lawyer than me. I also concede that he relies on some legislation of which I was unaware at lunchtime. But I still think he (and if they have adopted his argument the Scottish Parliament Corporate Body) are wrong, albeit with regard to sections of the 2016 Scotland Act not yet commenced.
The Prof has pointed out that by virtue of an obscure piece of legislation, "The Scotland Act 1998 (Modification of Schedules 4 and 5) Order 2015 the Scottish Parliament had, in 2015, been given the power to amend the date of the next Scottish Parliament Election. I readily concede I didn't know that, although the Prof himself was good enough to link to the Hansard debate in which it was clearly intended as a temporary measure. But while I might excuse myself from ignorance of an obscure Statutory Instrument the Prof also drew attention to The Scottish Election (Dates) Act 2016 of which I should have been aware earlier. For it uses the devolved competence of the 2015 Order to fix the date of the next Scottish Election as 6th May 2021.
But I don't think the Prof is interpreting things properly (ducks).
Because the 2015 Order was clearly intended as a temporary measure pending what became the Scotland Act 2016. And it says something quite different.
Section 2 of the Scotland Act 1998 (the founding Statute) says
"The poll at subsequent ordinary general elections shall be held on the first Thursday in May in the fourth calendar year following that in which the previous ordinary general election was held, unless the day of the poll is determined by a proclamation under subsection (5)."
Section 5 of the Scotland Act 2016 amends that.
I've tried unsuccessfully formatting and reformatting this to get it on the page so here is the link http://www.legislation.gov.uk/ukpga/2016/11/section/5/enacted
In summary the section (as amended) now reads
"The poll at subsequent ordinary general elections shall be held on the first Thursday in May in the fourth calendar year following that in which the previous ordinary general election was held unless
(a) subsection (2A) prevents the poll being held on that day......"
Subsection 2A reads
"The poll shall not be held on the same day as the poll at
(a) a Parliamentary General Election......"
I readily admit I've cut out a lot of irrelevant text here for brevity (and clarity) but if you doubt me, feel free to look at it for yourself.
Now, sections 4-10 of the Scotland Act 2016 have not yet been commenced but when they are they will become the law of the land. And they will then dictate when the next Scottish Parliament election will be, notwithstanding any Holyrood legislation. For, for the avoidance of any doubt on the matter, section 10(7) of the Scotland Act 2016 specifically revokes "The Scotland Act 1998 (Modification of Schedules 4 and 5) Order 2015".
So, in summary, if Sections 4-10 of the Scotland Act 2016 are commenced, the next Scottish Parliament Election will be on the first Thursday in May 2020. I stand by that argument.