It was briefly adopted by British forces in 1951, but the decision was overturned very shortly thereafter by Winston Churchill's incoming government in an effort to secure NATO standardisation of small arms and ammunition.

Although the Army had intended to replace the .303 on several occasions dating from before World War I, these efforts were repeatedly put off due to one crisis after another.

There had been some consideration of a less powerful cartridge just prior to the start of WWII, using a 7.92 mm bullet, but in the aftermath of the Dunkirk evacuation, any interest in this development ended.

[3] Inspired by the captured German Fallschirmjäger rifles 42 (FG 42), the aim was to develop a multifunctional weapon, called Light Automatic Gun (L.A.G.).

Military intelligence suggested that it would be ten years before the Soviets would be ready for another major war, so the time frame for re-equipping was the mid-to-late 1950s.

Experience during the war led to demands for a smaller "intermediate" sized cartridge that would allow fully automatic fire from a rifle-sized weapon.

After testing a variety of designs, they selected a bullet of about .270 in (6.9 mm) calibre and 1 inch (2.5 cm) long, with a mass of 130 grains (8.4 g).

By this time, Korsak had left the original EM-1 program and Kazimierz Januszewski had replaced him and had adopted the anglicized name Stefan Kenneth Janson.

The EM-1 used 0.04 in (1.02 mm) thick steel plate pressings for simpler manufacture, a roller locked short recoil mechanism, and was somewhat heavier at about 10 pounds (4.5 kg) with an empty magazine.

Winston Churchill felt a NATO standard was more important than any qualities of the weapon itself and overturned the decision by the previous Labour Minister of Defence, Manny Shinwell, who had already announced an intention to move to the .280 and the EM-2.

[13] It was clear the EM-2 could not be easily adapted to the powerful 7.62×51mm NATO round [citation needed], so the only realistic alternative was to adopt a licensed version of the FN FAL from Fabrique Nationale.

Some years afterwards, NATO also agreed to move to a smaller round more suitable for full-automatic fire and lighter weapons, ultimately adopting the 5.56×45mm.

[14] However, the revival of the EM-2 was short-lived as the 6.25mm was dropped for an even smaller 4.85mm cartridge in a completely new rifle, the L64/65 which evolved into the 5.56mm SA80 currently used by the British Army.