Developed by BSA immediately after World War Two, the No7 MkI training rifle was the only one of the British Enfield trainers to use a magazine. Only 2500 of these rifles were produced, contracted by the Royal Air Force and delivered in 1948. Their magazine is a commercial BSA 5-round magazine modified slightly to latch into a housing inside a regular No4 Enfield magazine body. This makes them a particularly enjoyable rifle for range shooting, as well as one of the scarcest of the standard British trainers.
Note that Canada also developed and adopted a No7 MkI .22 rimfire trainer, but that type is a single shot design, and does not share any parts with the British No7 MkI.