VOSA recently changed their ruling on checking ball joints. apparently they should now be checked with the vehicle in its driving position... i.e. not raised in the air (sorry maggers

) the fact that hes put it down as an advisory really wouldnt worry me in the slightest unless you have wandering steering or vagueness. get wifey/girlfriend (but dont let them meet each other) to shake the steering smoothly from left to right only about from 10o'clock to 2o'clock positions.
iirc you have a 1.6 so if you look down the back of the engine youll see a piece of equipment that looks like the item labelled (1) in the picture below.
coincidentally almost exactly where the marker for number (1) is, is almost the exact location of the inner ball joint, inside the ribbed gaitor.
now this will make more sense when your actually looking at it but your looking for a smooth transition in directional change when rocking the steering and looking at the relationship between the rack (silver bit) and the track rod (the thinner rod going out to each wheel) if it seems to 'clunk' or 'jump' then you have issues... you can also hold the track rod lightly and you would be able to feel if its 'clunky'... if its smooth then probably all is well.
if your unsure and have a half decent video recording on your phone video the movement and post it up and ill give you my professional opinion

bear in mind that MOT testers have to have x amount of fails compared to x amount of passes... they also tend to advise defects that aren't really all that major. when its all recorded by VOSA it looks a little bit more legit if they are failing a certain percentage and picking up defects on a certain percentage of vehicles. now thats not to say that theyre telling lies or fiddling the books but they may note things that are negligible. at the end of the day each tester will deem a certain defect in a different way. what one tester may deem as unsafe another may not and if its a specialist they may put it down to a certain marques characteristics and deem it not a defect at all.