accelerator lag on vauxhall corsa design "08"?

i drive a 6 month old vauxhall corsa design automatic. i have nearly had several accidents in it when pulling out onto a roundabout or onto a main road from a t junction. e.g. i pull up at t junction and want to turn left. there is a car coming but at a safe distance for me to pull out. i put my foot on the accelorator but nothing happens for about 2 seconds. the car then regains power but i am now pulling out with the oncoming car quite a bit closer but its too late for me to stop.sometimes it takes longer for the car to start moving and this can be quite dangerous. the car has been on a computer at a vauxhall dealership but they cant find anything wrong.