The 5th Middlesex Militia or Royal Elthorne Light Infantry was an auxiliary regiment raised in Middlesex in the Home counties of England just before the Crimean War. It later became part of the Middlesex Regiment. Primarily intended for home defence, it served in England and Ireland during Britain's major wars, and saw active service during the Second Boer War. It was converted to the Special Reserve under the Haldane Reforms and supplied reinforcements to the Royal Fusiliers' fighting battalions during World War I. After a shadowy postwar existence the unit was finally disbanded in 1953.