Hi,
Totally agree with above. No the info you were given is not correct. If you look at the "nutritional information" list on the label of each bottle you will see the "Total Carbohydrate" figure listed per 100ml. This is the overall amount of carbohydrate contained in the drink, either per 100ml or per bottle.
This is usually followed by "of which sugars" which shows how much of the total carbohydrate is made of sugar and will generally be a lower figure than the total Carbohydrate figure. (Only actual sugar would show the same figure in each section as all of the carbs in sugar are sugar).
The Total Carbohydrate is the important one to follow - it tell you how much carb there is in each 100ml that you will drink. In the case of Pepsi Max it is NIL (so there is no carbohydrate at all in the drink). I am sure that Diet Coke, Coke Zero and Diet Pepsi are all NIL in the Total Carbohydrate and so contain no sugar. If they did contain any amount of sugar it would be listed as "Total Carbohydrate" and also "of which sugars".
It is worth noting that some diet drinks do contain a lower amount of sugar than the non-diet version and also some can contain fruit sugars but will be marked as "No Added Sugar".
The nutritional information for Diet Coke:
http://www.coca-cola.co.uk/brands/categ ... -coke.html
Coke Zero:
http://www.coca-cola.co.uk/brands/coke-zero.html
And for Pepsi Max/Diet Pepsi:
http://www.pepsi.co.uk/Products/Default.aspx
Hope that doesn't make it too complicated. Basically, if the total carb shows NIL or TRACE it is sugar-free.