SSD, high AoA in the Gnat leads to lots of buffet and a high RoD. You would need to seriously abuse the aircraft very deliberately to induce a spin - the topic wasn't even covered in our AFTS course on the aircraft. The closest we flew to high AoA at low speed was the '100 kt recovery' - "Boot the black*, punch the white*, set 6° TPI, leave the throttle alone and wait...."
Flying in the back on an SCT formation tailchase was the only time I ever saw that drill used in anger - when the creamie QFI became disorientated in the vertical. Fortunately the drill worked as advertised.
While the Gnat has a very complicated longitudinal control system (with which all Gnat pilots must be fully conversant), it actually has very benign handling characteristics. Q-gearing and 'Cam K' make it more pleasant to fly at high speed than even the Hunter 6. A lovely little jet!
* - refers to the yaw dolls' eyes - the Gnat didn't have a 'turn and slip' gauge.