In the British tradition the Prerogative of Mercy is one of the historic Royal Prerogative

Royal Prerogative

The royal prerogative is a body of customary authority, privilege, and immunity, recognized in common law and, sometimes, in civil law jurisdictions possessing a monarchy as belonging to the sovereign alone. It is the means by which some of the executive powers of government, possessed by and...

s of the British monarch in which he or she can grant pardon

Pardon

Clemency means the forgiveness of a crime or the cancellation of the penalty associated with it. It is a general concept that encompasses several related procedures: pardoning, commutation, remission and reprieves...

s to convicted persons. In actual practice, this power has been delegated to the Secretary of State for Justice in England and Wales and the Scottish Ministers in Scotland.

The Royal Prerogative of Mercy was originally used to permit the monarch to withdraw death sentence

Death Sentence

Death Sentence is a short story by the American science-fiction writer Isaac Asimov. It was first published in the November 1943 issue of Astounding Science Fiction and reprinted in the 1972 collection The Early Asimov.-Plot summary:...

s, but is now used to change any sentence or penalty.

This Royal Prerogative power became reviewable by the courts in the key case of Derek Bentley

Derek Bentley

Derek William Bentley was a British teenager hanged for the murder of a police officer, committed in the course of a burglary attempt. The murder of the police officer was committed by a friend and accomplice of Bentley's, Christopher Craig, then aged 16. Bentley was convicted as a party to the...

.