Yes, changing down is normal under certain circumstances. It will happen if you are descending a steep hill and require extra engine breaking or accelerating hard. What is happening is something different. If I am cruising at a (hypothetical) speed of 75mph and accelerate when I lift off the speed drops normally but then the 'box changes down. I end up cruising at the set speed in fourth gear at which point I flick it up into fifth. I have had the car for four years and have covered a fair few long distance motorway miles in it whilst going on holiday and it has only just started doing this. I see that there are two control units for the CC. One electronic and the other which looks mechanical/electrical. I was wondering if one of these was faulty and if so which I should suspect first.