Replying to say this person is correct, it's a promise from Tesco that the food they'll provide in your online food shop will have a minimum of 4 days until best before/use by. It so if you buy 5 different proteins for example, they won't fuck you over and give you everything that goes out of date tomorrow
This is the main reason why I don't like doing online shopping. They give you all the shit that no-one in-person wants to buy; bruised fruit & veg, food with short shelf life. I'm a single guy, often have to freeze nearly everything I get online as otherwise it goes off before I can eat it all. 4 days is pathetic.
They usually have minimum spend too, so they literally want me to buy more food than I need then give me a load of food I can't eat in time.
How long it keeps. But as long as it's not meat or dairy produce, it'll be a "best before" not a "use by" date, and most stuff is usable long after its best before date. Those crumpets will be fine for at least a week, if you keep them in an airtight container or ziplock bag after opening. After that, they might be a bit stale, but still edible; warm them up nd put a bit of butter on, that'll soften them up nicely.