From a historical point of view top fermented ale (öl in Scandinavian) is the original beverage in Britain. Unlike Continental style bottom fermented beers it wasn’t hopped and during a period before one started using hops when brewing ale as well, and beer became the common word, that was one of the main distinctions between the two types.
There’s supposedly some benefit in giving nursing mothers beer to get the milk going for the bub.
Dad tells a story about when I (their first child) was born, and mum was having trouble feeding me. One of the nurses tipped him off to get mum some beer. Mum doesn’t drink, but she consented for medicinal purposes, and the breast milk flowed freely thereafter, luckily for me. Of course this was in rural Australia, in the seventies, so beer was probably prescribed for just about anything. 
Not strictly true, I’ve seen a number of UK pubs that chill glasses, but only for lager. Never for beer or real ales.
For the record, I much prefer ale to lager, unless I’m going for quantity over quality.
Bring back mead!
ETA: There are lots of “American-style” bars (as opposed to pubs) in London - especially around Richmond and Twickenham - where they serve American lagers in frosted glasses.
Or gruit!
Gruit was a precursor to hopped beer. Supposedly, gruit was made with various mildy-psychoactive ingredients such as mugwort & sweet myrtle. Then the church discovered that hops was a mild sedative and much preferred people getting numb than wacked-out, so they had the government start taxing every brew that was not made with hops. Soon, gruit died out.
Oddly enough ( or perhaps not ) the only time I’ve encountered some variety of honey mead in the recent past is in Ethiopian restaurants.
So basically, a stout is a stronger type of porter. Or, in other word, all stouts are porters but not all porters are stouts. (Correct me if I’m wrong.)
Another term you might come across is “small beer”. This was very weak beer (under 1%) and was consumed by men, women and children a couple of hundred years ago. Because of the brewing process it was safe to drink, and much safer than water.
I remember a news story not too long ago about small beer being served in Belgian schools, so it is still around.
As for Porter vs. Stout, I’ve here various differentiators. One that I go by is that Stout has roasted barley whereas Porter has just black patent malt. Not sure if that is historical revisionism but works better than to say some arbitrarily stronger brew is a stout (stronger than what?).
Historically, this was true. Currently, no. Both porters and stouts can range in the 4% abv to 10% up range. As I mentioned above, the main difference between porters and stouts, as the terms are used today, is that porters use dark malted barley for color and flavor, while stouts also use roasted unmalted barley, in addition to malted barley. This isn’t always true, though. A style known as Robust Porters sometimes will use roasted unmalted barley in the grain bill, too.
So, in general, it’s the presence of roasted unmalted barley that currently separates porters from stouts, although even that is not universal, with some porter styles using roasted unmalted barley. But there’s a lot of overlap.
If you want to read the technical definitions of the styles according to the Beer Judge Certification Program, you can read here:
Anchor Brewing sells small beer, and Goose Island Brewing in Chicago will occasionally have it on tap at their local pubs, as well. Small beers are made by doing a second running of water through a mash that has already been used to make a much stronger beer. So, say you’re brewing a porter. You keep your first runnings of the wort for the porter (and taking up most of the sugars and flavor with it). What’s left is a bed of grain that still has some sugars left in it. You run some water over that and get all the left overs and get a weaker, lighter product. It’s kind of like running a second pot of coffee through your coffee maker using the spent beans from the first pot.
Anchor and Goose Island small beers generally run at about 3% abv, but they use the runnings of some of their strongest beers (Anchor uses Old Foghorn Barleywine, 8-10% abv, as the base for their Small Beer.)
Thanks for the link to the BJCP pulykamell, lots of interesting stuff there, but some I don’t agree with.
If this is going to turn into a general beer question thread then I have one. Are bottle-conditioned beers available in North America? These have a little bit of yeast in the bottle so fermentation continues as in a cask-conditioned British Real Ale.
I have just found this interesting link about British beers from the past. Note the paragraph about the one-time popularity and dominance of mild (beer).
Bunches of them. At the moment, I’m partial to Boulevard. If you want something really oddball, Dog Fish will be right up your alley.
As Tapioca Dextrin mentioned, there’s oodles and oodles of bottle conditioned beers in America. You can look through this thread for a sampling. Not all of Dogfish Heads brews are bottle conditioned (actually, I don’t think most of them are, unless I’m mistaken) but they do make some bottle-conditioned ales like Squall.
And, yes, the BJCP is just guidelines for beer contests and the like. There’s going to be a good bit of overlap between styles, and not every brewery uses the same exact definitions to label their beers. Like I said, for me, if I brew a heavy malted beer, if it has roasted unmalted barley in it, I call it a stout. Otherwise, I call it a porter. If I were entering beer contests, I’d pay closer attention to the exact guidelines, but I don’t compete. I just drink. 
Whenever I order a beer (OK, ale) from a bar, I think of a scene in a Bob Hope/Bing Crosby road movie, where in the deep untamed North, in a wild everything-goes bar, Hope asks for a milk. Noticing the looks around him, he snarls, “In a dirty glass.”
Now that’s American.
Thanks for that link Rayne Man, v interesting. Watney’s red is before my time, but I’ve often wondered how such a rank ale could get so popular. Go for a pint in a decent alehouse and one is struck by the massive brewing heritage in the UK. But if we have all these breweries of note and character, what were they all selling in the 60s? Where was the quality ale being supped?
Anyone growing up in the Midlands just after the war will probably remember Davenports and their home delivery of beer. Once a week their vans used to come door-to-door delivering their beer. It came in screw-top pint bottles housed in a sturdy wooden crate.
This from their TV commercial:-
*Beer at home means Davenports!
That’s the beer!
Lots of cheer!
The finest malt with hops and yeast,
Turns a snack into a feast.
Straight from breweries to your home,
Why collect?
We’ll deliver!
Soon you’ll know why folks all say:
“Beer at home means DAVENPORTS “!*
I think of the scene early in the original version of *Get Carter *in which Michael Caine walks into a pub in Newcastle, orders a pint and then snaps his fingers at the barman and says, “In a thin glass.”