Policy Exchange said the UK Government should prevent the Bill, which was passed by MSPs before Christmas, from becoming law.
It said the legislation will redefine the meaning of “sex” under the Equality Act, with implications for single-sex spaces, associations and schools, as well as women-only shortlists and scholarships.
MSPs passed the Gender Recognition Reform (Scotland) Bill by 86 votes to 39, approving reforms which will allow trans people to obtain a gender recognition certificate (GRC) without the need for a medical diagnosis.
The Bill will also allow 16 and 17-year-olds to apply for a GRC for the first time, and would reduce the amount of time a person has to live in their acquired gender before they can be granted the document.
However, the move has sparked controversy, with concerns from some politicians, women’s rights groups and others that the changes could impact on safe spaces for females.
A report by Policy Exchange argues the legislation makes “a very significant change to the operation of the Equality Act in Scotland”, adding: “The Equality Act is reserved to Westminster and so the Scottish Parliament is not permitted to change its operation in Scotland.”
Written by Dr Michael Foran, a senior fellow at Policy Exchange and law lecturer at the University of Glasgow, the paper says the Bill will have implications for the operation of equality law throughout the UK.
It says the UK government is within its legal rights to make a section 35 order prohibiting the Bill from gaining royal assent in its current form.
A section 35 allows UK ministers to issue an order prohibiting Holyrood’s Presiding Officer from submitting a Bill for royal assent if there are reasonable grounds to believe it would adversely affect the operation of UK-wide equality legislation reserved to Westminster.
Prime Minister Rishi Sunak has said it is “completely reasonable” for the UK Government to consider the issue.
The new report says there “remains a genuine concern over the lack of adequate safeguarding in the Bill”, adding: “Yet, even without that concern, there would be substantial issues relating to the effect that the Bill will have on the operation of wider equality law throughout the UK.”
It adds: “On this basis alone, a section 35 order is justified. At a minimum, it cannot be denied that there are very complicated legal questions that need to be resolved if this Bill is to be workable. Additional time to sort out these complexities would be of great value in this context.
"Action is needed on the part of the UK and Scottish governments to resolve these issues and bring coherence to the law in this area. A section 35 order will give both governments the time needed to address issues which will affect both the operation of reserved matters in Scotland, and the implications that this will have for the rest of the UK.”
A foreword by Lord Keen, the former Advocate General for Scotland, says it would “not only be impractical but constitutionally improper for the UK Government to permit a devolved legislature to enact a provision that had a material impact upon the operation of the law throughout the United Kingdom”.
It adds: “The immediate concern identified by Dr Michael Foran is the potential impact of the Scottish Government’s gender recognition legislation upon the operation of the Equalities Act 2010, an Act which clearly addresses issues reserved to the UK Government and which operates throughout the UK. Such concerns were voiced during the passage of the Bill in the Scottish Parliament. It is therefore unfortunate that the position of the Scottish Government has remained opaque and at times contradictory.”
A Scottish Government spokesman said: “The Bill as passed is within legislative competence, and was backed by an overwhelming majority, with support from members of 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.
“We have always been clear that the Bill does not impact on the Equality Act, and the Bill as passed puts that position beyond doubt.”