Theresa May’s plan to implement Brexit without the authorisation of a vote in parliament would be “a contemporary necessity” rather than a misuse of outdated ancient royal powers, the attorney general said at the start of the most keenly awaited constitutional law case in recent memory.

Opening the government’s submission in front of the 11 justices of the supreme court, Jeremy Wright QC and MP told the highest court in the land that royal prerogative powers were an essential part of the UK’s unwritten constitution and could therefore legitimately be used to trigger article 50.