The Supreme Court of the United Kingdom unanimously ruled that advice given by Prime Minister Boris Johnson to Queen Elizabeth II that Parliament should be prorogued was unlawful.

The Supreme Court of the United Kingdom is the final court of appeal for all civil cases in the United Kingdom and all criminal cases originating in England, Wales and Northern Ireland, as well as some limited criminal cases from Scotland.

R (Miller) v The Prime Minister and Cherry v Advocate General for Scotland, also known as Miller II and Miller/Cherry, were joint landmark constitutional law cases on the limits of the power of royal prerogative to prorogue the Parliament of the United Kingdom. Argued before the Supreme Court of the United Kingdom in September 2019, the case concerned whether the advice given by the prime minister, Boris Johnson, to Queen Elizabeth II that Parliament should be prorogued in the prelude to the United Kingdom's withdrawal from the European Union was lawful.

Alexander Boris de Pfeffel Johnson is a British politician and writer who served as Prime Minister of the United Kingdom and Leader of the Conservative Party from 2019 to 2022. He was previously Foreign Secretary from 2016 to 2018 and Mayor of London from 2008 to 2016. He was Member of Parliament (MP) for Henley from 2001 to 2008 and for Uxbridge and South Ruislip from 2015 to 2023.

Elizabeth II was Queen of the United Kingdom and other Commonwealth realms from 6 February 1952 until her death. She had been queen regnant of 32 sovereign states during her lifetime and was the monarch of 15 realms at her death. Her reign of 70 years and 214 days is the longest of any British monarch, the second-longest of any sovereign state, and the longest of any queen regnant in history.