Inter-War period

In 1926 the British Army changed their nomenclature; the SMLE became known as the Rifle No. 1 Mk III or III*, with the original MLE and LEC becoming obsolete along with the earlier SMLE models. Many Mk III and III* rifles were converted to (.22 rimfire) calibre training rifles, and designated Rifle No. 2, of varying marks.

The SMLE design was fairly expensive to manufacture because of the many forging and machining operations required. In the 1920s several experiments were carried out to help with these problems, reducing the number of complex parts. The SMLE Mk V (later Rifle No. 1 Mk V), used a new receiver-mounted aperture sighting system, which moved the rear sight from its former position on the barrel. The increased gap resulted in an improved sighting radius, improving sighting accuracy, and the aperture improved speed of sighting (making it also known as a "battle sight"). The magazine cutoff was also reintroduced, and an additional band was added near the muzzle for additional strength during bayonet use. Unfortunately, this design was found to be even more complicated and expensive to manufacture than the Mk III, and so was not developed or issued beyond a trial production of this rifle numbered approximately 20,000 units, produced between 1922 and 1924 at RSAF Enfield. The No. 1 Mk VI also introduced a heavier "floating barrel" that was independent of the forearm, allowing the barrel to expand and contract without contacting the forearm and changing the zero of the rifle. The receiver-mounted rear sights and magazine cutoff were also present, and production numbered 1025 units, produced between 1930 and 1933.

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 Mk VI, 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. Towards the end of WWII, a bladed bayonet was developed and issued for the No 4 rifle, using the same mount as the spike bayonet.

During the course of World War II, the No. 4 rifle was further simplified for mass-production with the creation of the No. 4 Mk I* in 1942, which saw the bolt release catch removed in favour of a more simplified notch on the bolt track of the rifle's receiver. It was produced only in North America, with Long Branch Arsenal in Canada and Savage-Stevens Firearms in the USA producing the No. 4 Mk I* rifle from their respective factories. On the other hand, the No.4 Mk I rifle was primarily produced in the United Kingdom.

After World War II Great Britain continued to trial new self-loading rifles (SLR's) and a new service cartridge. However, nothing as yet was near troop trial stage. For now the No4 rifle would continue to serve as England's service rifle.

The Mk2 version of the No4 was approved in late 1947, this change addressed an accuracy problem discovered during the war. It was found that stock warpage, due to changing weather or climate conditions would adversely effect the trigger pull of the rifle. As in all previous Lee-Enfields the trigger was hung from the triggerguard and the triggerguard rested on the underside of the fore-end independent of the receiver. A modification that moved the anchor/pivot point of the trigger from the triggerguard to the receiver was used to correct this problem. In conducting this modification the fore-end was altered slightly to accommodate the addition of the mounting bosses to the receiver. The reinforcing strap and the center piece of wood was removed from the fore-end and a tie screw installed in its place. This screw readily identifies the Mk2 at a glance.

With this modification current issue No4 MkI and MkI* rifles could be retrofitted to the new design. This resulted in the No4 Mk1/2 (No4 MkI's altered to Mk2 configuration), No4 Mk1/3 (No4 MkI*'s altered to Mk2 configuration) and the No4 Mk2 (new manufactured).

Approved in late 1947, production continued until 1955. With these dates in mind, all No4 Mk2's were produced post-war from new billets making them free of any wartime economies. Many of these rifles were confined to storage until being released for surplus and can still be found in excellent repair.