1. A motor vehicle having: a prime mover means; at least first and second groups of one or more wheels; and a driveline operable to connect the prime mover means to the first and second groups of one or more wheels such that the first group and not the second group of one or more wheels is driven by the prime mover means when the driveline is in a first mode of operation and the first and second groups are driven by the prime mover means when the driveline is in a second mode of operation, the driveline including an auxiliary portion comprising releasable torque transmitting means by means of which the driveline is operable under control of a controller to connect the second group of one or more wheels to the prime mover means when the driveline transitions from the first mode to the second mode, wherein when in the first mode the driveline is operable to transition to the second mode under the control of the controller, the controller being actuable to cause a transition of the driveline from the first mode to the second mode responsive to an output of a reactive evaluator indicative of a current need to assume the second mode, the controller being further actuable to cause a transition from the first mode to the second mode responsive to an output of a predictive evaluator indicative of a likely need to assume the second mode within a prescribed period of time, the output of the reactive evaluator being responsive to a determination whether an amount of wheel slip has exceeded a first prescribed threshold, the output of the predictive evaluator being responsive to a determination whether one or more conditions in respect of one or more vehicle operating parameters are met when the amount of wheel slip is below the first prescribed threshold, the controller being further actuable to cause a transition of the driveline from the first mode to the second mode at a rate responsive to at least one of the outputs of said reactive evaluator and said predictive evaluator, and wherein when the predictive evaluator determines that the second mode should be assumed, the predictive evaluator is arranged to provide the output indicative of the rate at which the transition from the first mode to the second mode should be made.