An energy recovery system for a vehicle having a shaft rotatable about a shaft axis and an engine arranged to drive one or more wheels, the energy recovery system including: a compressor having: a swashplate member; and one or more piston and cylinder assemblies, each having an air outlet for outputting a compressed air supply, either the piston or the cylinder of each piston and cylinder assembly being coupled to the swashplate member, and each piston and cylinder assembly being aligned with a compressor axis, wherein the swashplate member is able to tilt relative to the compressor axis between a no-compression position in which movement of each piston within its respective cylinder is prevented and a maximum compression position in which movement of each piston within its respective cylinder between a top dead centre position and a first bottom dead centre position is permitted, and wherein the swashplate member is arranged to be coupled to the shaft of the vehicle so that the compressor axis is substantially aligned with the shaft axis and so that the swashplate member is able to rotate in tandem with the shaft; a first air tank arranged to receive compressed air from the air outlets of the one or more piston and cylinder assemblies; and a motor arranged to expand compressed air from the first air tank to extract mechanical work for delivery to the one or more wheels of the vehicle, characterised in that: the swashplate member is able to tilt relative to the compressor axis between the no-compression position, the maximum compression position and an intermediate compression position in which movement of each piston within its respective cylinder is permitted between the top dead centre position and a second bottom dead centre position between the top dead centre position and the first bottom dead centre position; and in the no-compression position of the swashplate member each piston is located at the top dead centre position within its respective cylinder. a compressor having: a swashplate member; and one or more piston and cylinder assemblies, each having an air outlet for outputting a compressed air supply, either the piston or the cylinder of each piston and cylinder assembly being coupled to the swashplate member, and each piston and cylinder assembly being aligned with a compressor axis, wherein the swashplate member is able to tilt relative to the compressor axis between a no-compression position in which movement of each piston within its respective cylinder is prevented and a maximum compression position in which movement of each piston within its respective cylinder between a top dead centre position and a first bottom dead centre position is permitted, and wherein the swashplate member is arranged to be coupled to the shaft of the vehicle so that the compressor axis is substantially aligned with the shaft axis and so that the swashplate member is able to rotate in tandem with the shaft; a swashplate member; and one or more piston and cylinder assemblies, each having an air outlet for outputting a compressed air supply, either the piston or the cylinder of each piston and cylinder assembly being coupled to the swashplate member, and each piston and cylinder assembly being aligned with a compressor axis, wherein the swashplate member is able to tilt relative to the compressor axis between a no-compression position in which movement of each piston within its respective cylinder is prevented and a maximum compression position in which movement of each piston within its respective cylinder between a top dead centre position and a first bottom dead centre position is permitted, and wherein the swashplate member is arranged to be coupled to the shaft of the vehicle so that the compressor axis is substantially aligned with the shaft axis and so that the swashplate member is able to rotate in tandem with the shaft; a first air tank arranged to receive compressed air from the air outlets of the one or more piston and cylinder assemblies; and a motor arranged to expand compressed air from the first air tank to extract mechanical work for delivery to the one or more wheels of the vehicle, characterised in that: the swashplate member is able to tilt relative to the compressor axis between the no-compression position, the maximum compression position and an intermediate compression position in which movement of each piston within its respective cylinder is permitted between the top dead centre position and a second bottom dead centre position between the top dead centre position and the first bottom dead centre position; and in the no-compression position of the swashplate member each piston is located at the top dead centre position within its respective cylinder. the swashplate member is able to tilt relative to the compressor axis between the no-compression position, the maximum compression position and an intermediate compression position in which movement of each piston within its respective cylinder is permitted between the top dead centre position and a second bottom dead centre position between the top dead centre position and the first bottom dead centre position; and in the no-compression position of the swashplate member each piston is located at the top dead centre position within its respective cylinder.