The Metropolitan Police arrested six people in conjunction with an alleged terrorist plot to release ricin on the London Underground, although no toxin was found.

The Metropolitan Police Service (MPS), commonly known as the Metropolitan Police, and simply known as the Met Police or the Met, is the territorial police force responsible for law enforcement and crime prevention within Greater London. In addition, it is responsible for specialised tasks throughout the United Kingdom, such as dealing with counter-terrorism throughout the UK, and the protection of certain individuals, including the monarch, royal family, governmental officials, and other designated figures. It is also referred to as an eponym as Scotland Yard or the Yard, after the location of its original headquarters in Great Scotland Yard, Whitehall, in the 19th century. The Met is presently headquartered at New Scotland Yard, on the Victoria Embankment.

The Wood Green ricin plot was an alleged bioterrorism plot to attack the London Underground with ricin poison. The Metropolitan Police Service arrested six suspects on 5 January 2003, with one more arrested two days later.

Ricin ( RY-sin) is a lectin (a carbohydrate-binding protein) and a highly potent toxin produced in the seeds of the castor oil plant, Ricinus communis. The median lethal dose (LD₅₀) of ricin for mice is around 22 micrograms per kilogram of body mass via intraperitoneal injection. Oral exposure to ricin is far less toxic. An estimated lethal oral dose in humans is approximately one milligram per kilogram of body mass.

The London Underground is a rapid transit system serving Greater London and some parts of the adjacent home counties of Buckinghamshire, Essex and Hertfordshire in England.