Rishi Sunak has said it would be “completely reasonable” for his Government to consider legally challenging Scotland’s gender recognition reforms – a move that would be “unprecedented in the history of devolution”, according to a legal expert.

On Thursday, the Scottish Parliament overwhelmingly voted in favour, 86 to 39, of the Bill.

But Alister Jack, the Scottish Secretary, announced yesterday afternoon that the UK Government would consider using powers under the Scotland Act to prevent the Bill becoming law.

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As routine after any piece of Holyrood legislation, the UK Government has a four-week period to review any Bill agreed by MSPs before it moves to Royal Assent.

Under the Scotland Act, a section 33 can be used to refer Holyrood legislation to the Supreme Court if it the Advocate General for Scotland believes it is outwith the competence of the Scottish Parliament.

This has been used three times before – the Scottish Government’s UN Convention of the Right of the Child Bill, which is still to be revised, the European Charter of Local Self-Government and the EU Continuity Bill.

But Mr Jack yesterday pointed to a section 35 order being used, which would allow him to lay an order essentially vetoing the legislation.

The section 35 order acknowledges the legislation is devolved but would block its progress if the UK Government believes it could have an adverse impact on legislation reserved to the UK.

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A legal expert has set out the “two distinct paths” for the UK Government to apply to the courts to “review or attempt to block a Scottish Bill”.

Speaking to The Herald, Dr Andrew Tickell, devolved law expert at Glasgow Caledonian University, said: “First, if UK law officers think legislation is outside Holyrood’s legislative competence, they can refer the contested provisions directly to the Supreme Court to determine whether it ‘relates to a reserved matter’.

“This procedure has been used by the UK Government increasingly since Brexit.

“The second route to arresting the progress of a Bill is unprecedented in the history of devolution.

“Section 35 of the Scotland Act gives the Secretary of State the power to make an order, preventing the presiding officer from submitting a Bill for royal assent if they have ‘reasonable grounds to believe’ provisions of a Scottish Bill would be incompatible with the UK’s international obligations, or where a Bill would ‘make modifications of the law as it applies to reserved matters and which 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’.”

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He added: “If such an order is made, it has to be in writing, identify the provisions concerned, and explain their reasoning.

“Though section 35 has been in the Scotland Act since 1998, this has never happened before.

"After the passage of a Bill, the UK Government has a four-week window under the Scotland Act to take either step.”

The UK Government is believed to hold concerns that the gender recognition reforms could cut across the UK Equalities Act.

An amendment agreed at stage two of the Holyrood legislation process, put on the face of the gender recognition reform Bill, a statement that streeses it does not impact on the UK legislation.

Mr Sunak has now broken his silence on whether or not the UK Government will challenge the legislation.

He said: “Lots of people have got concerns about this new Bill in Scotland, about the impact it will have on women’s and children’s safety.

“So I think it is completely reasonable for the UK Government to have a look at it, understand what the consequences are for women and children’s safety in the rest of the UK, and then decide on what the appropriate course of action is.”

Speaking on BBC Good Morning Scotland, SNP Civil Justice Secretary, Shona Robison, insisted “the Bill as passed is absolutely within legislative competence”.

She added: “I think that any attempt by the UK Government to undermine what after all is the democratic will of the Scottish Parliament, will be vigorously contested by the Scottish Government.

“The legislation makes no change to the reserved Equality Act 2010 and that principle was actually enshrined within the Bill.

“So we are very confident of our position and it would be unfortunate, to say the least, if the UK Government was to go down this road.”

Mr Robison pointed to the last three days of gruelling debate of amendments where she “resisted” changes that could open up the legislation to legal challenge.

She added: “We didn’t want to put anything in the Bill that could rusk rubbing up against the 2010 Equalities Act that was unhelpful.”