If you're just joining us, here is a quick catch-up of the main points to come out of yesterday's Court of Session hearing.

• Scotland's top law officer, Lord Advocate Dorothy Bain KC, said the UK government's block on Scottish gender recognition reforms was unlawful
• She said the Court of Session has a "constitutional duty" to review the unprecedented use of a Section 35 Order by Downing Street
• The lord advocate insisted the Scottish Secretary's intervention to veto the bill was politically motivated
• If the UK government is successful, Westminster "could veto practically any act of the Scottish Parliament", Dorothy Bain warned
• Scottish Secretary Alister Jack has raised concerns that it would affect the 2010 Equality Act, which applies in Scotland, England and Wales

You can read a report from yesterday's session here.

The UK government used Section 35 of the Scotland Act to prevent the Gender Recognition Reform Bill receiving royal assent.

Scottish Secretary Alister Jack raised concerns that it would affect the 2010 Equality Act, which applies in Scotland, England and Wales.

David Johnston KC is presenting the UK government's case.

Image source, PA Media

This is the first time since the advent of devolution that the UK government has used a Section 35 Order.

It was issued on the basis that UK Ministers think the gender reform bill will have a negative impact on British law.

In this case, the law is the 2010 Equality Act, which MSPs are not allowed to change.

The 2010 Act applies in Scotland, England and Wales, setting out different "protected characteristics" including those of sex and gender reassignment, and underpins the rights and protections afforded to these groups.

UK Ministers have successfully challenged Holyrood legislation before - but on the basis that MSPs have exceeded their powers.

The bottom line is that the Scottish government wants to make it easier for people to change their legally-recognised gender.

It argues that the current process is too difficult and invasive, and causes distress to an already marginalised and vulnerable minority group.

Its plans would see applications handled by the Registrar General for Scotland, rather than the UK panel.

No diagnosis or medical reports would be required, and the period in which applicants need to have lived in their acquired gender would be cut to three months.

One of the Scottish government's most contentious proposals is to lower the minimum age that someone can apply from 18 to 16 - although 16 and 17-year-olds would need to have lived as their acquired gender for six months rather than three.

Image source, Getty Images

People currently have to apply, external to a UK gender recognition panel.

They will be asked to present a diagnosis of gender dysphoria.

This is defined by the NHS, external as being caused by a "mismatch" between their biological sex (whether they were born physically male or female) and their gender identity (the way in which they see and describe themselves).

Applicants need to provide two medical reports, one from a specialist detailing their diagnosis and another listing any treatment or surgery they may have had to change their sexual characteristics.

They must also prove they have lived full-time in their acquired gender for at least two years - for example showing they have used a different name in official documents, or changed their gender on their driving licence or passport - and swear an oath that they intend to continue for the rest of their lives.

Two gender recognition systems 'highly problematic' says Johnstonpublished at 10:12 British Summer Time 20 September 2023

10:12 BST 20 September 2023

The UK government argues it is "highly problematic" to have two different gender recognition systems within the UK.

It cites several potential issues, including with single-sex organisations, schools and tax rules. Such arguments have been contested by the Scottish government.

Opening his arguments on Tuesday, David Johnston KC said it was not Scotland Secretary Alister Jack's "duty" to scrutinise the bill as MSPs do, but to "protect the interests of the United Kingdom if he identifies adverse effects on the operation of law as it applies to reserved matters".

The lawyer described Section 35 as "integral to the constitutional distribution of power in the Scotland Act". He said it was "express recognition" that devolved bills could have an adverse effect on the operation of reserved law and that the UK government should have limited power to intervene if that happens.

David Johnston KC, who is acting for the UK government, gets today's proceedings under way.

Remember you can watch the court proceedings by clicking on the play icon at the top of this page.

Analysispublished at 10:01 British Summer Time 20 September 2023

10:01 BST 20 September 2023

Philip Sim
BBC Scotland political correspondent

The debate in court is tightly focused on interpretation of section 35 of the Scotland Act.

But the potential implications of the case go far beyond a paper argument.

One is that it will decide whether the reforms to the gender recognition process go ahead and take effect.

The debate over the merits of that – of making life easier for trans people, and the potential for impact on the rights of women and girls – has been very well rehearsed.

The Scottish government had hoped that passing the bill could help to move that debate along, both politically and perhaps in society too.

And there are constitutional implications too. The precedent set here will give us a better idea of the precise limits of the veto power conferred on UK ministers by section 35.

That in turn could inform the circumstances in which the power could be used again in future.

Image source, Legal argument will begin at the Court of Session in Edinburgh today

MSPs voted in December last year to pass the bill by 86 votes to 39.

So far, so straightforward? Not quite.

Scottish Secretary Alister Jack used UK government powers to veto the bill, saying it could interfere with equalities law across the whole country.

Scottish ministers then lodged a legal challenge at the Court of Session in a bid to overturn that decision and to have the reforms come in to law.

So this is the second day of legal argument to decide who is right and who is wrong.

Image source, PA Media

Here's a quick recap of yesterday's proceedings:

Scotland's top law officer said the UK government's block on Scottish gender recognition reforms was unlawful.

The Scottish government is seeking to overturn the veto at the Court of Session in Edinburgh.

Lord Advocate Dorothy Bain said the court had a "constitutional duty" to review the unprecedented use of a Section 35 Order by Downing Street.

The UK government has raised concerns about the impact of the legislation on Britain-wide equality laws.

David Johnston KC, who is acting for the UK government, urged the court to reject the Scottish government's petition.

• Read more here
• Scottish government challenges gender reform block
• Court clash over move to block gender reforms

Good morning and welcome to our live coverage of the latest developments with the Scottish government's controversial Gender Recognition (Reform) Bill.

We will bring you rolling updates and analysis as the Scottish and UK governments face off at the Court of Session in Edinburgh, for the second day.

The bill would make to make it easier for people in Scotland to change their legally-recognised gender.

But it has proved hugely controversial - leading to this legal challenge.