UK ministers have triggered powers to block the Scottish Government’s gender recognition reforms by using an unprecedented legal mechanism – in a move branded a "full-frontal attack" on devolution by Nicola Sturgeon.

MSPs overwhelmingly backed plans last month that will remove the need for trans people to require a gender dysphoria diagnosis to obtain a gender recognition certificate.

The move to a self-ID model, used by several other countries, also speeds up the process and reduces the lower age limit to 16.

The legislation was backed by all political parties at Holyrood except the Scottish Conservatives who supported the reforms under Ruth Davidson's leadership.

Scottish Secretary Alister Jack has now set out his intention to use Section 35 of the Scotland Act to pause the Holyrood reforms over concerns it impacts on UK-wide legislation.

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Nicola Sturgeon has warned the step puts the authority of the Scottish Parliament at risk and "its ability to make its own decisions on devolved matters".

She added that the Scottish Government "will defend the legislation and stand up for Scotland’s parliament".

The FM said: "If this Westminster veto succeeds, it will be first of many."

The move came after Ms Sturgeon earlier accused Tory ministers of using trans people “as a political weapon” – an accusation rejected by the UK Government.

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Mr Jack said that "after thorough and careful consideration of all the relevant advice and the policy implications", he was "concerned that this legislation would have an adverse impact on the operation of Great Britain-wide equalities legislation".

He said: “Transgender people who are going through the process to change their legal sex deserve our respect, support and understanding.

"My decision today is about the legislation’s consequences for the operation of GB-wide equalities protections and other reserved matters."

Mr Jack stressed that he has "not taken this decision lightly".

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He added: "The Bill would have a significant impact on, amongst other things, GB-wide equalities matters in Scotland, England and Wales.

"I have concluded, therefore, that this is the necessary and correct course of action.

“If the Scottish Government chooses to bring an amended Bill back for reconsideration in the Scottish Parliament, I hope we can work together to find a constructive way forward that both respects devolution and the operation of UK Parliament legislation."

The Scottish Secretary has written to the Speaker of the Commons, Holyrood’s presiding officer and the First Minister, informing them of his intention to use a Section 35 order.

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It is likely Mr Jack will issue a statement in the House of Commons today on the matter while the official order will set out the reasoning behind the UK Government's move.

Section 35 of the Scotland Act states that an intervention can be made if the Secretary of State “has reasonable grounds to believe would have an adverse effect on the operation of the law as it applies to reserved matters”.

If enacted, the Section 35 would need to go through the House of Commons and the Scottish Government is likely to launch a judicial review in the courts to challenge the decision.

A Section 35 has never been used by the UK Government to hold up Holyrood legislation before by essentially stopping the process reaching royal assent.

UK Government sources have indicated the concerns relate to both the 2004 UK Gender Reform Act that first put in place a process for trans people to obtain a gender recognition certificate as well as the 2010 Equality Act.

The Equality Act allows circumstances where a single-sex space can prevent, limit or modify trans people’s access to a service.

But SNP Social Justice Secretary, Shona Robison, who led the proposals through Holyrood, branded Mr Jack’s action as “an outrageous decision”, adding it was “a dark day for trans rights and a dark day for democracy in the UK”.

HeraldScotland: Shona RobisonShona Robison (Image: PA)

Ms Robison said: “This is a political decision that is more in keeping with UK Government’s contempt for devolution and the Scottish Parliament.

“We have always been clear that the Bill does not impact on the Equality Act. The UK Government had multiple opportunities to comment during the extensive consultation on the Bill and during its passage and we are confident that the legislation as passed is within legislative competence of the Scottish Parliament.

“We will examine the reasons which the UK Government give for their order once we have them, but take whatever steps we can to ensure that the democratic will of the Scottish Parliament is not frustrated.”

But Scottish Tories equalities spokesperson, Rachael Hamilton, claimed the Scottish Government’s “decision to rush through flawed legislation at breakneck speed left the UK Government with little option” but to make a Section 35 order.

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She added: "“In their desperation to force this legislation through Holyrood before Christmas, the Scottish Government ignored the warnings that the Bill would have implications beyond Scotland’s borders.

“This unprecedented action was forced upon the Secretary of State because the scope of the bill reaches beyond the competency of the Scottish Parliament.

“I hope, rather than turning this issue into a constitutional football, the First Minister will now revisit this legislation.”

Labour's position on the action by the UK Government remains unclear after Sir Keir Starmer appeared to contradict Scottish Labour's position on opposing any interference from the UK Government.

Labour's shadow Scottish secretary, Ian Murray, said: “The Tory and SNP Governments must not use this for political posturing, but instead get round the table and find workable solutions that address legitimate concerns."

LGBT groups have branded Mr Jack’s decision “unacceptable” for trans rights.

Vic Valentine, manager of Scottish Trans, said: “The Bill as passed would introduce a simpler and fairer way for trans men and women to be legally recognised as who they truly are, allowing them to live with the dignity we all deserve.

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“For the UK Government to seek to block the Scottish democratic process in this way, simply because they disagree with the welcome decision the Scottish Parliament has made to improve trans people’s lives, is unacceptable. We fully expect the Scottish Government to challenge this in the courts.”

Stonewall warned that the UK Government has used the “nuclear option”, which was “an unprecedented move which significantly undermines the devolution settlement and will unlock constitutional and diplomatic strife”.

A spokesperson added: “This is now a constitutional matter between the UK Government and the Scottish Government.

“It is a matter of grave and profound regret that the Prime Minister has allowed trans people’s lives to be used as a political football.

“This is not governing with compassion. These are not the actions of a government that can stand on the international stage as a credible defender of LGBTQ+ rights.

“We hope that the legal process concludes swiftly, and that governments of the UK focus their attention on positive strategies that support LGBTQ+ communities to thrive.”