Dress no 1 Blue with pants Royal Horse Artillery 1939 (Uitgaans tenue met broek Royal Horse Artillery 1939)

No. 1 Dress, sometimes referred to as "blues", is a universal ceremonial uniform which is almost consistent throughout the British Army. No. 1 Dress is only worn on ceremonial occasions, and, in some regiments, by the duty officer. It is also regularly required to be worn by a short list of other units, senior staff officers, and officers appointed as aides to the Royal Family[15] and to the personal staff of senior officers in command. The order is not generally issued to all units, with the khaki No. 2 Dress functioning as the main parade uniform.

The origins of No 1 Dress can be traced back to various "undress", "patrol" or "frock" uniforms worn for semi-formal or ordinary duty occasions in the late 19th century. In its present form it dates from an order of dress issued at the time of the 1937 Coronation, intended as a cheaper alternative to the full dress uniforms that had been generally withdrawn after 1914. In 1947 a trial issue of what was now termed No 1 Dress was made with regimental distinctions as detailed below. Army units participating in the 1953 Coronation wore the new uniform as a temporary issue.

For most regiments and corps No. 1 dress consists of a dark blue tunic and trousers or overalls (or skirt) with a coloured peaked cap. Females should wear normal dark coloured tights when needed. Different units are distinguished by the colouring of the cap, piping on the tunic and of the welts or stripes on the trousers, as well as badges and in certain Cavalry Regiments by the colour of the collar.