The threat from Scottish Secretary Alister Jack almost immediately followed the Scottish Parliament’s overwhelming backing of the Gender Recognition Reform Act.
MSPs passed the controversial legislation, which has driven toxic debate and led to splits in almost every major Scottish political party, including the SNP, by 86 votes to 39 on Thursday afternoon.
The Bill will make it easier for transgender people to legally change their gender and was voted through following a marathon week of parliamentary scrutiny.
The SNP suffered their biggest rebellion in the history of the Scottish Parliament for the second time in the Bill’s passage, with nine rebels on the Government benches, including former minister, Ash Regan, voting against the legislation.
Scottish Labour also saw two of their junior spokespeople resign after breaking the whip and voting against the Bill.
Claire Baker and Carol Mochan, Scottish Labour’s spokespeople for drugs and mental health respectively, immediately resigned their positions following the vote. Michael Marra, the party’s education spokesperson, and Pauline McNeill, the party’s justice spokesperson, were both provided with leaves of absence to enable them to avoid the vote.
The Scottish Conservatives, who gave their MSPs a free vote, saw three members back the Bill – two more than at stage one.
Now passed, the Bill, should it gain royal assent, will lower the minimum age for those seeking a gender recognition certificate to 16 and drops the time required for an applicant to live in their acquired gender from two years to three months – six for those aged 16 and 17 – though with a three-month reflection period.
It also removes the need for a medical diagnosis of gender dysphoria to obtain the certificate.
However, the UK Government immediately intervened and suggested it could employ never-before-utilised powers within the Scotland Act to block the Bill in the Supreme Court.
Section 35 of the Scotland Act allows the UK Government to intervene and block passage of a Bill if it the UK Government believes it makes modifications to the law on reserved matters or has an adverse effect on the operation of the law around reserved matters.
Such a move would be unprecedented and would highly likely result in another Supreme Court case pitting Westminster against Holyrood.
In a statement after the final vote, Mr Jack said the UK Government would consider action in the Supreme Court.
“We share the concerns that many people have regarding certain aspects of this Bill and, in particular, the safety issues for women and children,” Mr Jack said.
“We will look closely at that, and also the ramifications for the 2010 Equality Act and other UK-wide legislation, in the coming weeks – up to and including a section 35 order stopping the Bill going for Royal Assent if necessary.”
However, Shona Robison, the Cabinet secretary for social justice, said it would be “very disappointing” if the Bill was blocked following the “decisive” vote in favour.
She said: “It would be very disappointing if the UK Government didn’t respect Scottish democracy and the decision of the Scottish Parliament.
“This area of policy is entirely within devolved competence.”
A Scottish Government spokesman later added: “The Bill as passed is within legislative competence, and was backed by an overwhelming majority, with support from all parties.
“Any attempt by the UK Government to undermine the democratic will of the Scottish Parliament will be vigorously contested by the Scottish Government.”
Ms Robison said the debate had mainly been respectful, but there had been “a bit of filibustering”.
This was echoed by Nicola Sturgeon during First Minister’s Questions when she accused the Scottish Conservatives of seeking to delay the vote deliberately.
Ms Sturgeon told MSPs in answer to a question from Tory MSP Sue Webber that “some of the elements of our proceedings this week have reflected badly on the Conservative Party”.
“I recognise different and sincerely held views on this Bill, but not withstanding that what we saw from the Conservative Party were deliberate attempts to filibuster, to delay and to frustrate the decision making process,” she said.
The SNP leader also told Scottish Tories counterpart Douglas Ross earlier that she would “always stand up for women’s rights”, adding: “But I am proud of the fact that, this afternoon, Parliament will, I hope, vote for a piece of legislation that will make the lives of trans people in this country that little bit better and easier, and I think that that is something to be proud of.”
Mr Ross had said the Bill “reduces women’s rights and, potentially, risk’s women’s safety”, adding that “a majority of the public oppose the Bill”.
Speaking in the final debate on the Bill on Thursday, Ms Robison said: “Every party in this chamber except one made a clear commitment to the reforms set out in this Bill at the last Scottish election, and at the one before that it was all parties.
“Trans rights are not in competition with women’s rights and, as so often before, we can improve things for everyone when those discriminated against act as allies, not opponents.”
The SNP Cabinet secretary also accused an unnamed MSP of calling a trans person an “it”.
But Scottish Conservative MSP Rachael Hamilton said the Bill “has shown this Parliament at its worst”.
She said: “In the rush to make the process a little easier for trans people, the Government is making it easier for criminal men to attack women. That’s the problem here.”
Labour’s Pam Duncan-Glancy said the legislation provided MSPs with “one of those rare moments … where we all have a real opportunity to improve lives and directly tackle inequality”.
She said the Bill would help “society to accept them [trans people] and to support them to be their best selves, without barriers or additional costs or medicalisation”.
The debate was briefly interrupted during Ms Robison’s closing speech when protesters opposing the Bill shouted “lies” as the minister was speaking.
Another shouted “I am a duck trapped in a women’s body. Quack quack, quack quack”.
Following the final vote, parts of the gallery cheered and applauded the result before opposing protesters shouted “shame at you” at MSPs. One appeared to flash the Chamber in the presence of minors after shouting “if you are not going to be decent, I am going to be indecent”.
Police Scotland said no arrest or complaint was made following the incident.