as iansoutham says its a good idea to have a hidden switch somewhere , i set one up on a mates lupo that was de-locked , basically a wire from the battery to the "unlock" feed in the central locking circuit with a push button switch in , i mounted it in the plastic arch liner as high up as i could and as the car was lowered it was difficult to get to and nobody knew it was there , got him out of the same situation a few times