In some cases, the British labels omit ingredients. For example, the British version of minestrone doesn't have chicken broth listed as the first ingredient, and I didn't see any other liquid listed that would make it into actual soup. American labels have to list ingredients in order of percentages, so you know the first item is the bulk of the product and the last items are there in trace amounts.

The Mountain Dew is a bad example. The American version has orange juice as the main flavor. The British version doesn't even identify what they use to flavor theirs.