Tractor with hybrid power system

An agricultural tractor comprising an internal combustion engine for delivering torque, wheels or tracks for imparting a propulsive force to the ground, and a power takeoff shaft for delivering torque to implements attached thereto, a mechanical drive connection between the engine and the power takeoff shaft, an electrical generator drivingly connected to the engine, and at least one electrical motor arranged to deliver a propulsion force to the wheels or tracks, the at least one electrical motor being electrically connected to, and powered by, the electrical generator, characterised in that the tractor further comprises a battery connected to the electrical generator and to the electrical motor, and a first motor/generator which provides said electrical generator drivingly connected to the engine, and to which the battery is connected so that electrical energy can be passed therebetween, wherein the first motor/generator can operate as a motor so that the power takeoff shaft is at least partially powered by electrical energy from the battery, further comprising an auxiliary electrical motor drivingly connected, via an auxiliary clutch, to the mechanical drive connection between the engine and the power takeoff shaft, wherein when the auxiliary clutch is open the power takeoff shaft is driven by the auxiliary electrical motor which is electrically connected to, and powered by, the electrical generator, wherein the auxiliary electrical motor is a motor/generator which can serve as a generator when the auxiliary clutch is closed.