The Ministry of Defence Police (MDP) is a civilian special police force which is part of the United Kingdom's Ministry of Defence. The MDP's primary responsibilities are to provide armed security and counter terrorism services to designated high-risk areas, as well as uniformed policing and limited investigative services to Ministry of Defence property, personnel, and installations throughout the United Kingdom. The MDP are not military police. Service personnel often refer to the MDP by the nickname "MOD plod".

Special police usually describes a police force or unit within a police force whose duties and responsibilities are significantly different from other forces in the same country or from other police in the same force, although there is no consistent international definition. A special constable, in most cases, is not a member of a special police force (SPF); in countries in the Commonwealth of Nations and often elsewhere, a special constable is a voluntary or part-time member of a national or local police force or a person involved in law enforcement who is not a police officer but has some of the powers of a police officer.