A surgical instrument 77 comprises an elongate shaft which terminates in an end effector which has two pairs of spaced apart opposable jaws 82,83 & 84,85, independently operable to cause the jaws of that pair to grip or release an object located therebetween, such as a length of suturing thread 70 which is to be passed behind another length of thread 71 when tying a suture around tissue during laparoscopic surgery. The jaws of each pair are movable to an open configuration in which that set of jaws is fully proximal of a point half-way along the length of those jaws when closed and in their most distally extended configuration. The method involves gripping the thread 70 first in trailing jaws 84,85, passing it across thread 71 and then gripping it in leading jaws 82,83. The tool may be operated manually or using surgical robots.
