A fastening system suitable for attaching a cladding panel to a structural substrate comprising: a first and second panel support profile member, each of the first and second panel support profile members comprising a first arm, a second arm and a bridging portion intermediate the first and second arm. The bridging portion is configured to be attachable to either a cladding panel or a structural substrate. The first arm of each of the first and second panel support profile members further comprises a projecting member; wherein the configuration of the second arm and at least a portion of the bridging portion of each of the first and second panel support profile member defines a recess; and wherein the first and second panel support profile members seat together such that the first and second panel support profile members interlock.