The British went into the 1880s with plans to adopt the Enfield-Martini as its new rifle, a single shot Martini-action rifle with essentially a sidesaddle of ready-access cartridges on the side of the receiver. It would be chambered for a new .402 caliber black powder cartridge. However, the Small Arms Committee begin looking into the possibility of a magazine rifle instead, and trials of 40+ different systems found three worth considering: a Lee rifle with a box magazine, a Lee rifle with a Bethel Burton magazine, and the Owen Jones rifle. As these trials were concluding, the discovery of smokeless powder threw a wrench in the plans.

After study of the Swiss 7.5x53.5mm cartridge, the British opted to develop a small bore .30 caliber round themselves, which would be the .303 British. This round, originally loaded with compressed black powder before the use of cordite, rendered the plans for the .402 caliber Enfield Martini obsolete. What would have been a justifiable territorial and reserve rifle alongside a .402 magazine rifle was now an orphan. With the new rifle in .303 caliber, a .402 single shot Martini was just an added logistical overhead. Instead, existing Martini rifles would eventually be converted to .303 British.

At any rate, the Lee rifle and magazine were chosen as ideal, and in 1888 a batch was made for field trials across the British Empire. Widely positive reports led to its formal adoption and the beginning of production in 1889 as the Magazine Rifle MkI - later retroactively renamed the Lee Metford MkI and colloquially known as the Long Lee. The example we have today has two very rare original features; an intact manual safety and Lewes pattern sights. Both of these would be quickly removed or replaced in service, and a Mk I* and MkII pattern followed shortly after the adoption of the MkI.