Parts of two bills passed by the Scottish Parliament must receive “further consideration”, Supreme Court justices have ruled.

Judges said on Wednesday that sections of the United Nations Convention on the Rights of the Child (Incorporation) (Scotland) Bill and the European Charter of Local Self-Government (Incorporation) (Scotland) Bill “would be outside the legislative competence of the Scottish Parliament”.

Lawyers representing the Attorney General and Advocate General for Scotland had asked Supreme Court judges to consider legal issues relating to the bills.

Judges were asked to consider whether the two bills could give Scottish courts “unparalleled” powers to strike down legislation from the UK Parliament.

They said the bills would return to the Scottish Parliament so issues could receive further consideration.

Five Supreme Court judges, who are based in London, had considered arguments at a hearing in June.

A barrister representing the Attorney General, and the Advocate General for Scotland, told the court that the case concerned “whether the Scottish Parliament has the legislative competence to subject acts of the UK Parliament with the need to comply with the UNCRC and to assign or delegate to the Scottish courts powers to strike down, rewrite or declare incompatible provisions of the acts of the sovereign UK Parliament”.

Sir James Eadie QC said: “Both bills, in slightly different ways, purport to bestow upon the Scottish courts extensive and, in part, unparalleled powers to interpret and to scrutinise the legality of primary legislation passed by the sovereign UK Parliament at Westminster.”

Judges were told that the UK Government had said its concerns were “not about the substance of the legislation” but whether the Scottish Parliament had the legal ability to pass the bills.

Judges said, in a summary of their ruling, that a section of the Scotland Act preserved the unqualified power of the UK Parliament to make laws for Scotland.

They concluded that three provisions of United Nations Convention on the Rights of the Child (Incorporation) (Scotland) Bill, and two provisions of the European Charter of Local Self-Government (Incorporation) (Scotland) Bill, would “fall outside the legislative competence of the Scottish Parliament”.

Judges heard that the Scottish Parliament had passed the bills in March.

“The bills are designed to give effect to two treaties to which the UK is a signatory: the United Nations Convention on the Rights of the Child (“the UNCRC”) and the European Charter of Local Self-Government (“the ECLSG”),” said one judge, Lord Reed, in a written ruling.

“The UNCRC was ratified by the UK in 1991.

“It is reflected in a number of provisions of domestic law, but has not been incorporated as a whole.

“The UNCRC Bill would incorporate a version of the UNCRC as scheduled to the bill.

“The ECLSG was ratified by the UK in 1998.

“It too is reflected in a number of provisions of domestic law, but has not been incorporated as a whole.

“The ECLSG bill would incorporate a version of the ECLSG as scheduled to the bill.”