An injection device comprising: a plunger for expressing medicament from a syringe, the plunger being provided with an enlarged head at a rearward end; an actuation mechanism arranged in use to provide a biasing force to urge the plunger from a first rearward position to a second forward position to express a dose of medicament; a latch member comprising an aperture through which the rearward end of the plunger extends in its rearward position so as to be retained against the force of the actuation mechanism; and a trigger for releasing the plunger from the latch member; one of the latch member and the trigger is provided with a substantially radially projecting member which is arranged to engage an opposing surface of the other of the trigger and the latch member; and characterised in that the latch member is arranged to at least partially radially displace and is radially segmented by at least a pair of opposing axially extending slots to provide two or more opposing segments; and the aperture is provided in a transverse wall at the rear of the latch member with the slots joining at the transverse wall and the slots being conjoined with the aperture such that the aperture expands when the latch member is radially displaced to release the enlarged head of the plunger; and wherein the trigger is moveable between a primed position in which the member and opposing surface prevent radial displacement of the latch member and a release position in which the radially projecting member moves clear of the opposing surface to allow displacement of the latch. a plunger for expressing medicament from a syringe, the plunger being provided with an enlarged head at a rearward end; an actuation mechanism arranged in use to provide a biasing force to urge the plunger from a first rearward position to a second forward position to express a dose of medicament; a latch member comprising an aperture through which the rearward end of the plunger extends in its rearward position so as to be retained against the force of the actuation mechanism; and a trigger for releasing the plunger from the latch member; one of the latch member and the trigger is provided with a substantially radially projecting member which is arranged to engage an opposing surface of the other of the trigger and the latch member; and characterised in that the latch member is arranged to at least partially radially displace and is radially segmented by at least a pair of opposing axially extending slots to provide two or more opposing segments; and the aperture is provided in a transverse wall at the rear of the latch member with the slots joining at the transverse wall and the slots being conjoined with the aperture such that the aperture expands when the latch member is radially displaced to release the enlarged head of the plunger; and wherein the trigger is moveable between a primed position in which the member and opposing surface prevent radial displacement of the latch member and a release position in which the radially projecting member moves clear of the opposing surface to allow displacement of the latch. a primed position in which the member and opposing surface prevent radial displacement of the latch member and a release position in which the radially projecting member moves clear of the opposing surface to allow displacement of the latch.