A British company called the Southern Gun Company (SCG) has developed a semi-semi-automatic AR-15 rifle action they call the Lever Release. After a round is fired the bolt always locks back and to release it (and chamber a new round) a lever, located opposite the selector on the left side of the lower receiver, must be actuated. Because this lever must be manually toggled to load a new round in the chamber, the UK does not class this as a semi-automatic rifle and is therefor easier to own by regular folk. The rifle is demonstrated in the video below …

Many thanks to Jacob for the tip.