In some countries it is just a law that almost everything has to have such a "best before" date.
And of course the companies selling those products choose a date where it is VERY unlikely the product is already bad, if handled correctly.
Expired dairy products (except some sorts of cheese) should be checked carefully, but in most cases they are still good for a few days after expiring.
As Quarto said: Beef lasts considerably longer than pork or chicken, and even if it is already "bad" you are not likely to get sick because you eat it. Pork is a bit more problematic (still lasts at least some days if expired when properly cooled) and chicken is not recommended.
Vegetables and fruits are also OK for some days (some of them for a week) although super markets throw them away already. Bananas for example: People tend to not buy them (so markets throw them away) if they have brown spots, but IMO that's just when they start tasting good!
So, if you're strapped for cash, it's a good idea to buy discounted near-expired foods from the nearby supermarket.
That's a very good tip!
I don't know if such a thing exists in England, though. In some countries people are more picky about food than in others. I have seen German supermarkets who have a "almost expired" discount shelf while an American told me he hasn't ever seen such a thing.
Canned food lasts VERY long. I would be a bit reluctant eating 20 years old stuff (which means checking if it smells wrong and maybe tasting a small part of it), although it is likely that even that is still good. I have eaten canned stuff that was two or three years expired a couple of times and I never got ill or something.