A lockable telescopic actuator arranged to be in a locked state or in an unlocked state, the lockable telescopic actuator comprising: a body defining a cylindrical cavity; a piston mounted to slide telescopically in the cylindrical cavity; and a locking mechanism comprising a first locking segment, the first locking segment arranged to move from a locked position to an unlocked position, wherein in the locked position the first locking segment is engaged with the piston to prevent the piston from moving relative to the body and in the unlocked position the first locking segment is disengaged from the piston to allow the piston to move relative to the body; and a first shape memory alloy, SMA, biasing element configured to be selectively extended or compressed, the first SMA biasing element arranged such that when the first SMA biasing element is selectively compressed the first locking element is biased into the locked position and when the first SMA bias element is selectively extended the first locking element is biased into the unlocked position.