Triggering article 50 without consulting the devolved assemblies in Cardiff, Edinburgh and Belfast would dissolve “the glue” that holds together the UK’s unwritten constitution, the supreme court has been told.
On the final day of the four-day hearing, the 11 justices have been hearing arguments about the significance of the Sewel convention.
The convention says that if Westminster is introducing legislation on issues that have been devolved it “normally” has to seek the consent of the devolved assemblies in Edinburgh, Belfast and Cardiff.
Richard Gordon QC, for the Welsh government, told the court: “The force of the Sewel convention is not its legal enforceability but that it’s a dialogue between legislatures.
“If the [UK government’s] prerogative powers can be used to short-circuit this dialogue, it’s to ignore the modern dynamic which we now have.
“A convention is a very important force in our society and it’s like the glue which can only hold an unwritten constitution together.”
Gordon dismissed the UK government’s argument that the Referendum Act 2015 gave ministers authorisation to trigger article 50, which formally signals the UK’s intention to leave the EU.
“The Referendum Act has nothing to do with the issues in this case,” he said. “It’s a statute that had died. It has fulfilled its purpose. You cannot revive a corpse by tearing up the death certificate.”