The Design Department of Enfield aimed to create a suitable submachine gun to suit the needs of the new General Staff Specifications that had been introduced in April 1945. This required that a submachine gun for the British Army was to fire at no more than 600 rounds per minute, have bayonet fittings for the British No.5 bayonet, have a magazine capacity of 30-60 rounds, and weigh no more than 6lb unloaded. Enfield's Design Department was then split into different sections; there were teams of Polish designers working on rifles and submachine guns, Belgian designers working only on rifles, and British designers who worked on all areas. The British team was headed by Harold J. Turpin, one of the designers of the STEN gun. Turpin's team created the MCEM1, whilst the Polish team, headed by Lt. Podsenkowski, created the MCEM2. The MCEM2 was very compact, at only 14 inches long. The magazine was inserted into the pistol grip to improve balance, the idea being that it could be fired like a pistol. The holster doubled as a shoulder stock, which could be attached to the rear end of the weapon. The bolt assembly was in a hollow cylinder 8 1⁄4 inches long, with a fixed firing pin that was 1 1/2 inches from the rear end. When fired, 7 inches of the 8-inch barrel were inside the bolt, and behind the bolt a fixed rod ejected protruded through the bolt face as the bolt returned. The magazine was 18 rounds and the fire rate was over 1000 rounds per minute. This meant that it did not meet the GS Specifications and could not be serviced, and it was rejected during the September 1946 trials.
Later the same year, Podsenkowski, assisted by Lt. Ichnatowicz, created an improved model known as the MCEM6. The barrel was lengthened and a bayonet lug was fitted. The weight of the bolt increased by 2oz and and the return spring was made heavier and longer. This meant the rate of fire was reduced to about 600 rounds per minute. Despite the improvements, all development of Podsenkowski's MCEM was cancelled in favour of Turpin's MCEM3, which showed "considerable promise". Just a year later, Turpin's weapon would also be cancelled.