The Westminster Trained Bands were a part-time military force established in 1572, recruited from residents of the City of Westminster. As part of the larger London Trained Bands, they were periodically embodied for home defence, such as during the 1588 Spanish Armada campaign. Although service was technically restricted to London, the Trained Bands formed a major portion of the Parliamentarian army in the early years of the First English Civil War. After the New Model Army was established in April 1645, they returned to their primary function of providing security for the palaces of Westminster and Whitehall. Following the 1660 Stuart Restoration, the City of London Militia Act 1662 brought them under the direct control of the Crown, with the Trained Bands becoming part of the British Army.

The London Trained Bands (LTBs) were a part-time military force in the City of London from 1559 until they were reconstituted as conventional Militia regiments in 1794. They were periodically embodied for home defence, for example in the army mustered at Tilbury during the Armada Campaign of 1588. They saw a great deal of active service during the English Civil War, including the First and Second Battles of Newbury, and the battles of Alton, Cheriton, Cropredy Bridge and Lostwithiel. Throughout their history they were used to suppress civil disorder and insurrection around the capital.