A controller for a parallel hybrid electric vehicle having a powertrain comprising an engine, electric propulsion means powered by energy storage means, and electric generator means operable to be driven by the engine to recharge the energy storage means, the controller being operable to: receive one or more signals indicative of one or more operating modes in which the vehicle is to be operated at a given moment in time, the one or more operating modes being selected from a plurality of operating modes including a selectable EV operating mode; receive a signal indicative of demanded powertrain drive torque; and cause the engine and electric propulsion means to deliver drive torque to one or more wheels to drive the vehicle in dependence on the signal indicative of demanded powertrain drive torque, the controller being operable to cause the powertrain to operate in a parallel powertrain mode in which when the vehicle is operating with the engine delivering drive torque to the one or more wheels the controller is operable to cause the electric propulsion means to apply drive torque to the one or more wheels in addition to the engine, the amount of torque delivered by the electric propulsion means being determined by the controller at least in part in dependence on the signal indicative of demanded powertrain drive torque and the one or more signals indicative of the one or more operating modes in which the vehicle is to be operated; the controller being further operable to cause the powertrain to operate in a parallel torque filling mode in which the powertrain causes the electric propulsion means to apply drive torque to the one or more wheels in addition to the engine in order to meet powertrain torque demand more quickly when an amount of powertrain demanded torque is less than a maximum steady state engine torque but exceeds the instant amount of torque developed by the engine, wherein the drive torque applied by the electric propulsion means when the powertrain is operated in parallel torque filling mode is different when the vehicle is in the SEV operating mode compared to the other operating modes of the vehicle. receive one or more signals indicative of one or more operating modes in which the vehicle is to be operated at a given moment in time, the one or more operating modes being selected from a plurality of operating modes including a selectable EV operating mode; receive a signal indicative of demanded powertrain drive torque; and cause the engine and electric propulsion means to deliver drive torque to one or more wheels to drive the vehicle in dependence on the signal indicative of demanded powertrain drive torque, the controller being operable to cause the powertrain to operate in a parallel powertrain mode in which when the vehicle is operating with the engine delivering drive torque to the one or more wheels the controller is operable to cause the electric propulsion means to apply drive torque to the one or more wheels in addition to the engine, the amount of torque delivered by the electric propulsion means being determined by the controller at least in part in dependence on the signal indicative of demanded powertrain drive torque and the one or more signals indicative of the one or more operating modes in which the vehicle is to be operated; the controller being further operable to cause the powertrain to operate in a parallel torque filling mode in which the powertrain causes the electric propulsion means to apply drive torque to the one or more wheels in addition to the engine in order to meet powertrain torque demand more quickly when an amount of powertrain demanded torque is less than a maximum steady state engine torque but exceeds the instant amount of torque developed by the engine, wherein the drive torque applied by the electric propulsion means when the powertrain is operated in parallel torque filling mode is different when the vehicle is in the SEV operating mode compared to the other operating modes of the vehicle.