If you're just joining us or need a recap here are the key points from the statement on the Scottish government's gender reform legal action:

• The Scottish government has set out the thinking behind its legal challenge to Westminster's block on its controversial gender identity plans
• Social Justice Secretary Minister Shirley-Anne Sommerville told Holyrood the move was "not taken lightly"
• MSPs voted in December last year to pass the Gender Recognition Reform Bill by 86 votes to 39
• But the UK government decided to block the reforms using a Section 35 order for the first time
• Sommerville said the government was acting in defence of Scottish democracy
• She said the Scottish government's petition for judicial review of the veto on the GRR Bill should be published tomorrow

• Scottish Conservative MSP Donald Cameron accused ministers of engaging in distraction from the "serious crisis that is currently engulfing the SNP"
• Labour MSP Paul O'Kane said he disagreed with the approach by Westminster, but said this escalating the row was not constructive

That's all from the live team today, thank you for joining us. The editors were Calum Watson and Deirdre Kelly. The writers were Paul O'Hare and Craig Hutchison.

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Scottish Conservative MSP Russell Findlay refers to the case of transgender rapist Isla Bryson, who was jailed for eight years in February for attacks on two women before changing gender.

He says the first minister previously said Bryson was "at it" and asks Somerville how the action will resolve what he describes as a "fundamental legal contradiction".

She replies by accusing Findlay of trying to connect the GRR bill with whether someone has a gender recognition certificate of not - which, she maintains, is not a valid argument.

SNP MSP John Mason asks the minister if the UK government's block means it could "veto any piece of legislation", including the Scottish government's budget?

Somerville went on to highlight Wales First Minister Mark Drakeford's concerns about the veto.

Philip Sim
BBC Scotland political correspondent

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The case will start at the Court of Session in Edinburgh, with a judicial review into whether Scottish Secretary Alister Jack was entitled to block the bill.

Judges will be tasked with deciding whether the order laid at Westminster has satisfied the strict conditions set out in the Scotland Act.

Those are that the Holyrood legislation "contains provisions which would make modifications of the law as it applies to reserved matters" and that Mr Jack had "reasonable grounds" to believe it would have an "adverse effect" on the operation of that law.

The Scottish government now says that UK ministers did not "provide sufficient justification" for the decision.

It is hard to predict exactly how the arguments will play out, because we are in completely uncharted territory.

There is no precedent to lean on in terms of which parts of that two-part test are more important, or how easy it might be to satisfy judges as to what "reasonable grounds" or an "adverse effect" really are.

But judges will no doubt be picking over the reasons set out in the order and the accompanying statement in great detail.

For all of the political rhetoric around this row, it is those points of law which will ultimately decide the fate of these reforms.

Read more here.

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Maggie Chapman says there was no meaningful engagement from the UK government on the GRR Bill and no amendments forthcoming.

The Green MSP says the UK government is acting in "bad faith" and she accuses the secretary of state of using the Section 35 order "as a weapon in the culture war against trans and wider LGBTQIA+ rights".

"I think this is an example very definitely of the UK government acting in bad faith," replies the minister.

SNP MSP Christine Grahame asks if litigation could be truncated to see if the bill could be amended to both parties satisfaction.

The minister replies she cannot comment on how the legal challenge would progress, but she points out that would not be a decision for the Scottish government.

Tory MSP Rachael Hamilton says this is an "unnecessary grievance" from the Scottish government that will not divert from the scandals tearing the SNP apart.

Ms Hamilton says the GRR Bill is "reckless" and again asks how much the SNP's court battle will cost.

The minister respondes by saying the easiest way to save money is for the UK government to revoke its section 35 order.

Analysispublished at 15:45 British Summer Time 19 April 2023

15:45 BST 19 April 2023

Philip Sim
BBC Scotland political correspondent

The most interesting thing we have learned today is that something will happen tomorrow.

The Scottish government is going to publish its petition – its application to the court containing the legal reasons why it believes the UK government was wrong to veto the gender reform bill.

Otherwise today has entirely been about scoring political points. It turned out to be a very familiar constitutional rammy about the standoff between the administrations in London and Edinburgh.

Ms Somerville told MSPs she could not discuss the legal arguments, despite the fact they will shortly be public knowledge.

But it is those legal points which will ultimately be crucial in deciding the fate of this legislation. When the court sits, all of the politics will be left at the door.

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Scottish Liberal Democrat leader Alex Cole-Hamilton asks if there has been any signal from the Scottish Secretary or his officials as to what would make the bill "competent" in their eyes.

Somerville says the sum total of discussions about potential amendments is "zero".

She adds it is "deeply disappointing" that Jack did not take up an invitation to discuss his concerns about the legislation.

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The social justice secretary tells the chamber: "We will be concerned because of the delay to this bill and the impact it is having on the trans community.

"I am deeply, deeply, sorry that it has come to this and we are not moving directly towards royal assent."

She points out it is not too late for a change of heart from the UK government and for it to withdraw the section 35 order.

The minister says she can't lay out a timetable for the court process.

Labour MSP Paul O'Kane says it is critical that MSPs don't lose sight of the purpose of the reform.

O'Kane says every day the bill spends in court is another day trans people don't have access to a reformed process.

He says the use of a Section 35 order was wrong and warns against allowing this to become a political football.

The Labour MSP asks how long the cabinet secretary thinks the bill will be in the courts and he asks what specific action the government is taking to support trans people.

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Cameron adds a lengthy and expensive legal action does not benefit those the bill is designed to help or the Scottish taxpayer.

The advocate also says the Scottish government was warned about the impact of the bill on the Equality Act during its passage but "ploughed on regardless".

He also calls on ministers to publish the legal advice they have received.

Somerville responds to Cameron that the cost of the legal challenge is a "matter of concern" and vows to publish the details once the action is completed.

She adds it is impossible to do so at this stage but pledges the government will be "very transparent" on the issue.

Donald Cameron, of the Scottish Conservatives, describes the Scottish government's legal challenge as "deeply disappointing".

He adds: "It is plainly doing so now to divert attention from the serious crisis that is currently engulfing the SNP."

Somerville warns that not challenging the order would "set a precedent that calls into question devolution itself".

She asks how long would it be before the UK government used the Section 35 order again?

This would gradually erode the hard-won devolved powers of Scotland, she says.

The social justice secretary says: "We will fight to protect the devolved competence and democratic function of this parliament and it is right that we do so."

The social justice secretary says the UK government has made no suggestion of changes to the bill.

Somerville says Secretary of State for Scotland Alister Jack used the Section 35 power in an unacceptable way that would have concerned even some Tories.

She says the order was used as "an absolute veto to strike down any devolved legislation passed by a majority of this parliament".

Somerville says Shona Robison offered a meeting with Alister Jack going forward, this was absolutely refused and Jack said there would be no future meetings on the issue.

She says Jack says two different regimes would create adverse affects.

"It has therefore proved impossible to find a way forward, or to consider a form of amended bill that this parliament would agree to and that would also lead the secretary of state to revoke the order."

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She continues the government's use of a Section 35 order was "the very opposite of a last resort".

Somerville goes on to accuse UK ministers of failing to raise any representations about the bill since it was first proposed by Scottish ministers in 2016.

And she claims it was stated back in 2018 that Scotland could adopt its own approach "if it wants to."

Somerville says the need for some powers around the Scotland Act is reflected in the memorandum of understanding between the UK government and devolved administrations, which was updated in 2013.

She says it clearly states that it contains provisions for the Secretary of State to intervene in devolved matters but that they should only be used very much "as a last resort".

Somerville says allowing the UK government's veto to go unchallenged would undermine this parliament's democracy.

The veto was used without prior warning, she adds.

The secretary of state has refused the offer to work on potential changes to the legislation, she says.

"The UK government has not offered up a single area for amendment."

The social justice secretary says parliament has already been informed about the petition for a judicial review of the secretary of state for Scotland's decision to make an order under Section 35 of the Scotland Act.

Shirley-Anne Somerville says there are strict limits as to what she can say.

She tells the chamber that the Scottish government has not taken the decision to challenge the order lightly.

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Social Justice Secretary Shirley-Anne Somerville will now deliver her statement on the challenge to the UK government’s Section 35 Order which has blocked the Gender Recognition Reform (Scotland) Bill from becoming law.

You can watch the statement by hitting the play icon at the top of this page and we'll bring you reports and analysis as we go.