The best before date indicates when food is at its best. Once this date has passed, the food may be in a less good condition. For example, crisps may have gone slightly stale. Food past its best before date is still safe to eat. Shops can sell food past its best before date.
Use by date marks are mostly used for foods that don’t last long, such as eggs, milk, bread, meat or fish. If you eat food that has passed its use by date you could be at risk of food poisoning. Shops are not allowed to sell food that has passed its use buy date.