you only really need to do the changing down gear and stuff when youre learning and in your test. when you pass, you'll find that its a lot easier and smoother to coast up to the roundabout, check what the other cars are doing, and then make a decision about whether youre going to stop or carry on. you have to remember that youre not going to get a major in your test for the car juddering as you approach a roundabout, the important thing is to concentrate on the other cars etc