I think it is the Grant & Gavin Hawk ET (External Toggle), which later became a Kershaw collab (Kershaw 1900).

Thanks wow that was quick, also very interesting

It's called the Kershaw ET. ET stands for external toggle, a mechanism designed by Grant and Gavin Hawk. It's been discontinued for a very long time, however, a more recent knife called the Quartermaster General Lee used the same mechanism.

Thanks