Seven Justices of the UK Supreme Court have begun hearing arguments over the validity of the Scottish Government's UK Withdrawal from the European Union (Legal Continuity) (Scotland) Bill.

The UK Government, through its Advocate General, has brought the challenge to the bill, which aims to keep Scottish law operating after Brexit day to the greatest extent possible in the same way as at present, as outwith the devolved powers of the Scottish Parliament. The UK and Scottish Governments have been at loggerheads over the extent to which each should acquire powers returning from the EU in otherwise devolved areas, and the bill conflicts in certain aspect with the EU Withdrawal Act passed by the UK Parliament and now on the statute book.

A written statement of the Scottish Government's case, sent to the Parliament by the Lord Advocate, James Wolffe QC, maintains that the existence of the UK bill was irrelevant to the Scottish Parliament's exercise of its own powers, as are policy arguments that the issue would be better dealt with at Westminster. It challenges the Advocate General's assertion that the bill relates to the reserved matter of international relations, arguing that it is directed at the domestic law consequemces of Brexit; and further maintains that to claim that the bill is "contrary to the constitutional framework underpinning the devolution settlement", or is "contrary to the rule of law principles of legality and certainty", are not questions that properly arise in a reference of this nature, posing a "legally irrelevant" question. In any event the bill is in keeping with that framework.

The Lord Advocate also challenges the grounds that the bill purports to modify the Scotland Act, and the European Communities Act 1972 – as it has been passed with regard to the context of withdrawal from the EU: its provisions are "directed to respecting the supremacy of EU law, by ensuring that there cannot be any temporal overlap between a provision of, or made under, the Scottish bill and any EU law with which that provision would be incompatible".

The Welsh and Northern Irish devolved administrations have lodged written interventions supportiung the Scottish Government's position.

Judgment is not expected until late in the year.