Sell by: This is information for the retailer and helps with their stock rotation and ordering. It doesn't really tell us anything about the nature or quality of the food.
Display until: Again, aimed at the retailer and to do with stocking and re-ordering levels.
Made on / produced on: At first glance this looks like useful information for the customer. If a sandwich shop is selling ham rolls freshly made today alongside those freshly made yesterday, which would you buy? However, today's rolls might be made with exactly the same ham, bread and other ingredients that were used yesterday. Sometimes these statements are just a little bit of clever marketing, as we naturally equate "freshly made" with "better quality". My favourite example is Budweiser - every bottle is stamped with a "born on" date. How cute is that! But what useful information does it give us about the product? None really. Production dates ARE useful, though, to manufacturers and distributors. If there is a problem with an item the batch can be quickly traced and, if necessary, recalled from sale and investigated.
Best before: This is to do with quality; consumers can expect the food to be in the best possible condition before this date. Once the date passes, though, the food is not inherently unsafe - it just might not be as crispy, crunchy, fizzy, tasty or whatever. You'll find best before dates on pre-packed non-perishable foods (cans, packets, boxes, jars etc). It's up to the manufacturer to come up with a reasonable best before date based on their own research and knowledge of the product. In reality, I suspect many manufacturers chose a shorter period than strictly necessary to insulate themselves against complaints about the quality or taste of their product.
Use by: This is the only date that has anything to do with food safety and so is the only one consumers really need to worry about. There are use-by dates on highly perishable foods, as there's a realistic risk that after this date any food poisoning bacteria naturally present may have multiplied to dangerous numbers.
Because best before and use by dates are the only ones with anything useful to tell the consumer, they're the only ones required under EU law. Manufacturers must label non-perishable foods with a best before date and high-risk, highly perishable foods with a use by date. It's perfectly legal to sell food past it's best before date, although you must make sure that the customer is aware of this, but it's an offence to sell food that's past it's use by date. Such food would be classed as "unfit for human consumption" in a catering context, even though you might cheerfully use it at home...
The current call to simplify date marking is the latest of many (here are just a few "news" stories from 2008, 2009, 2010, 2011 and 2013), but like the traffic-light nutrition labeling it's proved impossible to get major manufacturers and retailers to agree on a simpler system, especially as they find sell by, display until and produced on dates useful themselves. Successive governments have backed away from legislation following lobbying by the food industry giants, so I very much doubt whether anything will change in the near future.
Meanwhile, my Twitter feed is filling up with some fantastic projects for reducing food waste in your home, school or business. Have a look at the resources available from the Food Standards Agency, Love Food Hate Waste and WRAP for starters, and make sure you spread the word about the real meaning of all those date labels. And maybe, in spite of the industry big boys, we can all crack this dating game.