Highly perishable products have Use By dates. Examples are cooked meats, fresh meat, fresh fish, pies, salad packs, sandwiches. It is illegal for a shop to sell food past its Use By date. Food shouldn't be consumed past its Use By date as it is potentially a risk to health. Natrually manufacters of highly perishable products must ensure that the product will still be fit for consumption up to 23:59 on the day of expiry. In reality this means an item will normally be ok for a time afterwards (but this cannot be guaranteed and is not at all encouraged by the food industry).
Best Before dates are used on other types of food (there are a few exceptions such as salt, single ice cream and chewing gum which do not require Best Before dates). Fresh food will have a specific Best Before date, ambient products are usually marked Best Before End of a particular month. Consuming an item past its Best Before date is not a risk to health although the quality of the product might have suffered. Many retailers have recently started to use Best Before rather than Use By dates on fresh milk.
Sell By dates have not been a thing for around 25 years. These were previously used to indicate to a shop when an item should be removed from sale. They caused confusion for customers because Sell By dates had a margin built in so that a customer would have a few days to use a product after the Sell By date. The problem was many customers thought Sell By meant Use by.
Display Until is sometimes used in conjunction with Best Before to indicate to a shop when a product should be removed from sale. There will normally be a couple of days between Display Until and Use By so that the customer has a period of time to consume the product. Display Until is used on products like cut flowers to indicate when they should be removed from sale - many retailers have a guarantee that flowers will remain fresh for 7 days after purchase so the Display Until date has to take this into consideration.
Use By dates are not required on fresh fruit and veg. Instead fruit and veg must meet specific marketing standards (basically Class I or Class II). Best Before dates can be used to help meet these standards but there is no legal obligation to do so. Many retailers have decided to remove Best Before dates to reduce food waste.