Legal UK requirements:

Name: The name of the product must be clear 'Blackberry Yoghurt' must contain blackberries - if it does not contain the real fruit it must be clearly labelled 'Blackberry Flavoured Yoghurt'.
Datemark: 'Use by' means the product must be used by the date shown - never buy products past 'Use by' date - you may be inviting a health risk. 'Best before' means the product is still safe to eat after that date but the quality may be impaired. Weight: Must be clearly stated
List of ingredients: These must always be listed in order of weight with the largest amount first. Brand names and product marketing often include words such as 'Cheez' 'Buttery', 'Creamy' infering the contents contain mainly cheese, include butter & cream. Check the ingredients list, the words being used often describe texture or flavour and are not ingredients.
List of nutritional information: Energy, protein, carbohydrate, fat are usually listed by portion and also per 100 gms of product
Manufacturer: Useful information if you need to contact the manufacturer for further information
Source: This area is a bit of a mine-field. Some products are unambiguous - 'Grown in Kenya' means what it says. 'Sourced in the UK' can mean the product was grown and reared in the UK, or that a supplier in the UK ordered it! - it is the act of sourcing that is UK based, not the origin of the produce.
Health Claims: Foods sold proporting to be of specific benefits to health, must be proven to do just that. Many products are marketed with claims they may be benficial.
100% Pure: "Pure" is not regulated but consumers expect this to mean has nothing else in it. We do not expect to find additives in 'Pure Orange Drink' but check the ingredients which may read 'Made from pure oranges with added colouring' may also contain added sugars and preservatives - it is the orange juice that is pure not the drink! Likewise most 'Cranberry Juice Drink' are 50% water with as little as 22% actual cranberry juice, the word 'drink' in the name is the give-away that this is not all that it may seem.