During WWII, standard No. 4 rifles, selected for their accuracy during factory tests, were modified by the addition of a wooden cheek-piece, and telescopic sight mounts designed to accept a No. 32 3.5x telescopic sight. This particular sight progressed through three marks with the Mk 1 introduced in 1942, the Mk 2 in 1943 and finally the Mk 3 in 1944 (later somewhat confusingly re-designated the L1A1). Holland and Holland, the famous British sporting gun manufacturers, converted the majority of No 4 Mk I (T) sniper rifles, with the rest converted by BSA and, in Canada, Long Branch arsenal. These rifles were extensively employed in various conflicts until the late 1960s, and when the British military switched over to the 7.62x51 NATO round in the 1950s, many of the No 4 Mk I (T) sniper rifles were converted to the new calibre and designated L42A1.

The L42A1 sniper rifle continued as the British Army's standard sniper weapon until the mid 1980s, being replaced by Accuracy International's L96.

During the 1970s, RSAF Enfield produced the Enfield Enforcer series sniper rifles intended for use by police marksmen in Great Britain, though some were also exported. The Enfield Enforcer was made in unusually small numbers, a total of approximately 800 units. As a result, these rifles are highly sought after by firearms collectors, particularly since all stocks of Enfield Enforcers held by UK police forces were deliberately destroyed rather than reselling them.