A method for controlling a hybrid vehicle propulsion system that includes an internal combustion engine and an exhaust after treatment device for treating exhaust gases from the engine includes determining during operation of the vehicle a value of a parameter indicative of an efficiency of the exhaust after treatment device, identifying a vehicle operation cycle start event, determining during the operation of the vehicle an engine operation history characteristic for a time interval after the vehicle operation cycle start event, and determining whether or not to control the propulsion system so as to increase the efficiency of the exhaust after treatment device, in dependence on the determined exhaust after treatment device efficiency parameter value and the determined engine operation history characteristic.