I just read a section of a book written by a British author, and got much of the information for this post from this book. (I tried to change a few words here and there.) I mention this so that you don't attack me in case what follows turns out to be a pack of lies. Here's what to expect.
1. The first thing you will notice if you are simply wanting to go for a pint is that you can sit at a table until hell freezes over and never get a pint. This is because, in the main, British pubs don't have wandering waitresses in skimpy outfits who constantly hustle drinks. Don't know why. The Brits would sell a zillion more drinks if they didn't make you line up at the bar and plead with them to give them your money. So, one must assume the first difference between a pub and an American bar is that the Bar knows it is there primarily to take a lot of your money and to push drinks at you as fast as humanly possible. Admittedly, this story may just be a cruel hoax, perpetrated by said British author as an attempt at humor. It certainly doesn't seem logical to make your customers wait on themselves like that. If only because they won't want to do it very often.
2. Conversely, because you have no waitress, there is no waitress to tip everytime she brings a round of beer. (Although, in the UK, that would be called lager, probably.) You don't tip the bartender either. I know, I know. At those dry bars set up in the corner of wedding receptions, you are used to stuffing money in the big jar as you wait for him to hand you a bottle. Like he deserves a buck for taking the cap off for you, right? But in the UK, apparently there is no such tip jar. Very strange. And very cool indeed.
3. Don't be looking for frozen strawberry daiquiris. Pub barmen, as a rule, are not into mixing up exotic drinks. Nor are they likely to have a huge recipe book behind the bar as you find in the U.S. Beer. Wine. Vodka. Gin. Tequila. Whiskey (which they will spell whisky). And take it with a minimum of stuff in it, ok? Orange juice. Tonic water. A few other things. Not many.
4. Don't expect to be able to run a tab automatically. You pay as you go in Britain, unless you are known. Although, oddly, they will often take checks. But they will spell it ...... never mind.
5. Good news! Many pubs serve food. Actual real food, not just chicken wings in hot sauce or little beenie weenie sausages. No. Sandwiches. Hearty sandwiches. Yo! And pasties and OF COURSE....Fish and Chips. The bad news: it ain't free. Just as you would have to pay for a real meal in an American bar. But the Brits don't set out a bunch of free stuff for you pig out on, either.
Here are some words you had better learn if you are going to a pub or fast food place in the UK:
1. Bevvy (absolutely nothing to do with quail.)
2. Chippy (not a cheap whore.)
3. "My Shout" (actually, Americans don't have to learn this term since they would never do it.)
4. Scrumpy (hint: cider in the UK is never, or hardly ever, non-alcoholic. Definitely not what you think it is. And Scrumpy is the worst/best of the lot.
5. Starter (nothing to do with automobile parts or foot races.)
6. Take-away (not related to subtraction exercises)
And, of course, there are a few words that you as an American need to refrain from using. They won't know what you mean:
1. Appetizer (it simply isn't)
2. Bus Boy/bussing (simply not known)
3. Doggy bag (simply not used)
4. Tailgate party (simply not done)
5. Wet bar (a bar is a bar is a bar to a Brit)
6. 86 it (That will draw you some quizzical looks.)
But, holy hot tamales, is it ever fun. Worth the flight over there.