Supreme Court Unanimously Holds That Extended Prorogation Of Parliament Is Unlawful

In R (Miller) v The Prime Minister; Cherry and ors v Advocate General for Scotland [2019] UKSC 41, the Supreme Court found that the Prime Minister's advice to Her Majesty to prorogue Parliament for an extended period was unlawful and void, and quashed the consequent Order in Council effecting the prorogation.

Key Points

It is the function of the Court to determine the limits of prerogative powers, which can be by reference to common law principles. Parliamentary sovereignty and Parliamentary accountability are both common law constitutional principles which will be protected by the Court where necessary. The Government must provide a reasonable justification for any attempt to frustrate or prevent the exercising of these constitutional principles. Background

On 27 or 28 August 2019, the Prime Minister formally advised Her Majesty that Parliament should be prorogued for a period starting between 9 and 12 September until 14 October 2019. The Prime Minister announced the decision on 28 August 2019 and sent an explanatory letter to all MPs. An Order in Council effecting the prorogation was made that same day.

Mrs Miller immediately challenged the decision by way of judicial review and it was heard by the Divisional Court on 5 September 2019. The Court found against Mrs Miller but allowed her appeal to leap-frog to the Supreme Court.

Joanna Cherry QC MP and a cross party group of 75 MPs had separately, and pre-emptively, brought proceedings in Scotland on 30 July 2019 in relation to the same matter. The claim was initially dismissed by the Outer House of the Court of Session on the basis that it was not justiciable. It was then appealed to the Inner House of the Court of Session, where it was determined that the case was justiciable and, further, that the decision was unlawful as it had been tainted by improper purpose.

Both decisions were appealed to the Supreme Court and were heard by the Court on 17 - 19 September 2019.

A number of interveners also argued that prorogation was unlawful. These included The Right Honourable Sir John Major KG CH (for whom Herbert Smith Freehills acted), the Lord Advocate (on behalf of the Scottish Government), the Counsel General for Wales, Raymond McCord (a victims' campaigner in Northern Ireland), the Shadow Attorney General (Baroness Chakrabarti) and the Public Law Project.


The Supreme Court determined that the Prime Minister's advice to Her Majesty to prorogue Parliament was justiciable and, due to...

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