The remainder of the SA80 family comprises the L86 Light Support Weapon, the short-barrelled L22 carbine and the L98 Cadet rifle. The SA80 was the last in a long line of British weapons (including the Lee–Enfield family) to come from the Royal Small Arms Factory, the national arms development and production facility at Enfield Lock.
The system's history dates back to the late 1940s, when an ambitious programme to develop a new cartridge and new class of rifle was launched in the United Kingdom based on combat experience drawn from World War II. Two 7mm prototypes were built in a bullpup configuration, designated the EM-1 and EM-2. When NATO adopted the 7.62×51mm NATO rifle cartridge as the standard calibre for its service rifles, further development of these rifles was discontinued (the British Army chose to adopt the 7.62 mm L1A1 SLR semi-automatic rifle, which is a licence-built version of the Belgian FN FAL).
In 1969, the Enfield factory began work on a brand new family of weapons, chambered in a newly designed British 4.85×49mm intermediate cartridge. While the experimental weapon family was very different from the EM-2 in internal design and construction methods, its bullpup configuration with an optical sight was a clear influence on the design of what was to become the SA80. The system was to be composed of two weapons: the XL64E5 rifle (also called the Enfield Individual Weapon) and a light support weapon known as the XL65E4 light machine gun.
The sheet metal construction, and the design of the bolt, bolt carrier, guide rods, gas system and the weapon's disassembly showed strong similarities to the Armalite AR-18 which was manufactured under licence from 1975 to 1983 by the Sterling Armaments Company of Dagenham, Essex, and which had been tested by the UK MoD in 1966 and 1969.
During the development of the SA80, a bullpup conversion was made of an AR-18 and a Stoner 63 at Enfield due to the fact they could be used with stocks folded/without stocks which allowed the bullpup conversion and were later chambered in the experimental 4.85x49mm round. A bullpup conversion of the AR-15 was previously considered but the buffer tube in stock prevented the idea.