The Scottish government said on Wednesday that it will challenge the blocking of its controversial gender reform bill by the UK, paving the way for a legal showdown between the two administrations.
Scotland's Social Justice Secretary Shirley-Anne Somerville said that by preventing the Gender Recognition Reform Bill, which makes it easier for people to change their legally recognised gender, the UK government was setting a "dangerous constitutional precedent".
"The Gender Recognition Reform Bill was passed by an overwhelming majority of the Scottish Parliament, with support from members of all parties," Somerville said in a statement.
"The use of Section 35 is an unprecedented challenge to the Scottish Parliament's ability to legislate on clearly devolved matters and it risks setting a dangerous constitutional precedent."
Scotland Secretary Alister Jack said in January that he would use section 35 of the Scotland Act 1998 to prevent the bill from proceeding to Royal Assent, the final stage required to get proposed legislation onto the statute books.
He said he was concerned that the move by the devolved legislature in Edinburgh would negatively affect equalities legislation across England, Scotland and Wales.
Under devolution rules, which led to the establishment of the Scottish parliament in 1999, London can block legislation if ministers believe it will have an "adverse effect on the operation of the law".
Tense relations
The legislation, passed by the Scottish parliament in December, makes it easier and faster for people to officially change their gender, dropping the requirement for a gender dysphoria medical diagnosis.
It allows people aged 16 and 17 to change their gender, despite efforts by some Scottish lawmakers to keep the age at 18.
It also reduces from two years to three months - or six months for 16-17 year-olds - the time needed for an applicant to live in their new gender before it is officially recognised.
Jack said while transgender people who are going through the process to change their legal gender deserve respect, support and understanding, his decision was based on its legal implications.
The looming standoff over the gender law ratchets up London's tense relations with the Scottish government, which last year saw the ruling Scottish National Party's efforts to hold a new independence referendum stymied by the UK Supreme Court.
Opponents of the law fear it could present dangers to women and girls, particularly around the provision of single-sex spaces.
But the Scottish government insists it will not impact the UK's Equality Act, which allows for trans people to be excluded from single-sex spaces such as changing rooms and shelters.
"It is important to have clarity on the interpretation and scope of the Section 35 power and its impact on devolution," Sommerville said.
"These matters should be legally tested in the courts."