By the late 1930s the need for new rifles grew, and the Rifle, No. 4 Mk I was first issued in 1939 but not officially adopted until 1941. The No. 4 action was similar to the Rifle No.1 Mk.3 but lighter, stronger, and most importantly, easier to mass produce. Unlike the SMLE, the No 4 Lee-Enfield barrel protruded from the end of the forestock. The No. 4 rifle was considerably heavier than the No. 1 Mk. III, largely due to its heavier barrel and a new bayonet was designed to go with the rifle: a spike bayonet which was essentially a steel rod with a sharp point, and was nicknamed "pigsticker" by soldiers. Following the Halifax-Butler Coup, the British produced the No. 4 Mk.II , a refined and improved No. 4 rifle with the trigger hung from the receiver and not from the trigger guard, fitted with beech wood stocks (with the original reinforcing strap and center piece of wood in the rear of the forestock on the No.4 Mk I/Mk I* being removed in favour of a tie screw and nut) and brass buttplates. With the introduction of the No. 4 Mk.II rifle, the British refurbished all their existing stocks of No. 4 rifles and brought them up to the same standard as the No. 4 Mk.II.
In theory, the British Rifle .303 No.4 Mk.II equipped the British Army postwar but it was recognized as being hopelessly obsolete. Accordingly most units made use of salvaged German Stg.44 rifles with the No.4s being kept for parade use. Both weapons were replaced by the new L1A1 rifle in the late 1950s.