A gas turbine engine comprising: a first compressor; a second compressor coupled to a stub shaft; a starter generator coupled to the first compressor; and a clutch configured to selectively couple the first compressor and the second compressor, characterised in that the clutch comprises a clutch shaft coupled to the first compressor so as to always rotate with the first compressor, wherein the clutch shaft includes circumferentially spaced outer recesses; a stationary cage affixed to the clutch shaft, the stationary cage including a plurality of slots and ramps; an actuator cage rotatably positioned between the circumferentially spaced outer recesses of the clutch shaft and the stationary cage, wherein the stub shaft concentrically surrounds the clutch shaft, the actuator cage and the stationary cage; and rollers disposed within windows of the actuator cage; and a lever arm coupled to the clutch shaft; wherein, in an engaged state, the rollers are disposed within the slots of the stationary cage to rotationally couple the clutch shaft to the stub shaft; wherein, under centrifugal loading imposed on the lever arm by the clutch shaft rotating above a threshold speed, the lever arm pushes the actuator cage to move the rollers from the slots of the stationary cage and to between the ramps of the stationary cage and the outer recesses of the clutch shaft to thereby automatically disengage the stub shaft from the clutch shaft such that the second compressor freewheels above the threshold speed; and wherein, below the threshold speed, the clutch is automatically in the engaged state such that the second compressor rotates with the first compressor. a first compressor; a second compressor coupled to a stub shaft; a starter generator coupled to the first compressor; and a clutch configured to selectively couple the first compressor and the second compressor, characterised in that the clutch comprises a clutch shaft coupled to the first compressor so as to always rotate with the first compressor, wherein the clutch shaft includes circumferentially spaced outer recesses; a stationary cage affixed to the clutch shaft, the stationary cage including a plurality of slots and ramps; an actuator cage rotatably positioned between the circumferentially spaced outer recesses of the clutch shaft and the stationary cage, wherein the stub shaft concentrically surrounds the clutch shaft, the actuator cage and the stationary cage; and rollers disposed within windows of the actuator cage; and a lever arm coupled to the clutch shaft; wherein, in an engaged state, the rollers are disposed within the slots of the stationary cage to rotationally couple the clutch shaft to the stub shaft; wherein, under centrifugal loading imposed on the lever arm by the clutch shaft rotating above a threshold speed, the lever arm pushes the actuator cage to move the rollers from the slots of the stationary cage and to between the ramps of the stationary cage and the outer recesses of the clutch shaft to thereby automatically disengage the stub shaft from the clutch shaft such that the second compressor freewheels above the threshold speed; and wherein, below the threshold speed, the clutch is automatically in the engaged state such that the second compressor rotates with the first compressor.