This is what the Supreme Court will be considering today in a case expected to last 4 days. Follow it live here.
The case is about prerogative powers, defined by the High Court in the original case as “the residue of legal authority left in the hands of the Crown” however as the UK has a sovereign parliament it is argued that prerogative powers cannot be used to overrule legislation. The government argues, however, in does have the prerogative power to “make and unmake treaties” allowing it to launch the process without requiring an Act of Parliament.
The Scottish Government is also involved in this case. The Lord Advocate’s intervention proposes that triggering article 50 requires an Act of the UK Parliament and as a result requires a Legislative Consent Motion of the Scottish Parliament as matters devolved to them are involved.