An internal combustion engine comprising, an engine management unit, a combustion chamber having an inlet port and an outlet port, a fuel supply mechanism to supply gasoline to the engine, a valve train mechanism to permit introduction of air to the inlet port of the combustion chamber and release exhaust gases from the outlet port of the combustion chamber, and an external recirculating system whereby exhaust gases from the outlet port may be passed to the inlet port, wherein, the engine management unit is operable to, control the valve train mechanism to retain and/or rebreathe exhaust gases within the combustion chamber to cause the engine to operate in a controlled auto ignition combustion mode, and control the external recycling system to supply exhaust gases to the inlet port in the controlled auto ignition combustion mode, such that self-ignition occurs in the combustion chamber.