The distinction between Jam and Conserve in the UK is a result of the Trade Description act I think.
Like the diference between 'Fruit Juice' 'fruit drink' 'squash' etc.
To call something by a particular name it has to have more than a certain proportion of some relevant ingredient.
Shop jam hasn't got a very high fruit content, and not all might be the fruit named on the label. Conserve has a high % of fruit and is like home-made jam.

The shopper in the UK needs to study the law before shopping (or assume that you get what you pay for)