The invention relates to a controller for a hybrid electric vehicle having 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 a signal indicative of a required hybrid driving mode; receive a signal indicative of a state of charge of the energy storage means; determine which of a plurality of powertrain operating modes is appropriate for vehicle operation at a given moment, the powertrain operating modes including an engine charging mode in which the engine drives the generator means to recharge the energy storage means and an electric vehicle (EV) mode in which the engine is switched off and the electric propulsion means is operable to develop drive torque to drive the vehicle; and cause the powertrain to assume the appropriate powertrain operating mode and the required hybrid driving mode, wherein the controller is operable to determine which of the plurality of powertrain operating modes is appropriate for vehicle operation in dependence at least in part on the signal indicative of the instant state of charge of the energy storage means and a reference value of state of charge, the controller being operable to set the reference value of state of charge to one of a plurality of different respective values in dependence on the signal indicative of the required hybrid driving mode.