This question is bigger and more convoluted than you would realize. It is more like something you would write a term paper over in the university than a random question. I will basically answer it because I have written a paper about it, spoken with an American and a British accent, and traveled a lot, but you will only get a general picture on a blog.
All Americans know there are several accents within the United States alone. We have the southern accent that is very recognizable. We have the Bostonian accent, the New York accent, the California accent, the Ohio Valley accent, etc. England is the same way. Every part of England, in fact, sometimes different parts of London have different accents. There are times that two people, one with an American accent and the other with a British accent meet, and they may not even be able to understand one another, but there are times they will meet and even almost have the exact same accent. I was actually translating from English to English once when I was in the London subway. There was a woman from Wales and a man from the American Ohio Valley trying to speak, but couldn’t understand one another, but I understood both, so I was translating. I found it very funny. In fact, I knew two different guys from Yorkshire when I was in Romania. One of them spoke like I do and the other dropped his “h’s”, etc. and took a bit of getting used to before I easily understood everything he said. The guy who spoke like I do told me he used to speak like the guy who dropped his “h’s,” but that when they go to the university in England, they try to clean their English up and give them a more educated sounding English.
With saying all that, you can see why what I say has to be very general. You could write a book on all the different accents in each country. However, there are some major differences that are very general, but may not apply to every last person. Some major differences between America and England are the spelling of some words, expressions, word choice, and basic pronunciation.
In general, Americans like to say what is on the page unless they are from the south where they like to drop the final “g.”. British like to drop letters. At one time, from what I understand, the British didn’t drop their “r’s,” but there was a trend began, maybe beginning in the 1800’s, when they were trying to make a class difference, and the more sophisticated English began dropping their “r’s.” Now a days, most of them drop their “r’s,” and it became the accepted way that most people speak. In the more low class accents in England, they like to drop their “h’s” at the beginning of words when they speak. People from Ireland and American southerners often sound similar because they both drop the final “g” in words. I haven’t always been in the habit of dropping that final “g,” and in graduate school, a professor pulled me aside in Texas and told me people would be more comfortable if I would drop my final “g.” I had never thought much about it. I just always speak however I feel comfortable, but I learned that your accent can put other people at ease or make them feel strange. However, for the most part, the Americans like to pronounce exactly what is written on the page. Except for that final “g” or the Bostonians who also leave “r” out, American like to pronounce what they see, but British are more likely to leave letters out.
Another difference in pronunciation between America and England is the vowel sounds. Vowel sounds seem to have the biggest variations in America. Sometimes in England, the “a’s” are pronounced just like the California accent or the broadcasting system in America pronounces them, but sometimes, they are pronounced like “a” in “father” when they wouldn’t be in America. If you go to the southern part of the U. S., they elongate all their vowels. Instead of saying just “saying,” they would say “sa-ayeen.” The southerners in the U S. speak slower than everyone else. The British have a tendency to try to sound more sophisticated, and it makes a lot of Americans uncomfortable. However, many Americans laugh at the southerners. It isn’t just the southerners who butcher those vowels. In Washington State, instead of simple saying “bag,” (with the “a” like begins “apple”). they say “beg,” In England, many of the may say “bahg.” If you go to the Ohio Valley, there is an “o” they like to butcher. vowels seem to be more nebulous everywhere. I have never been around someone with the Bostonian accent, but I can really hear the strange number they do on vowels when I hear them on TV. Think about the way the Kennedy family speaks. President Kennedy and his brothers all have and had the Bostonian accent.
Another difference in pronunciation is that the British speak more clipped, and the Americans speak more relaxed. The British are very particular about the way their kids speak. That is why the one guy I knew was made to change his accent when he studied at the university. In England, there is a definite class difference that is detected when they speak. Americans don’t always worry about the class differences with their speech. Americans seem to measure one another on how much money they have thinking accents have nothing to do with class.
Besides pronunciation, there are some basic vocabulary words as well as spellings that are different between England and America too. One good example is how I used the word “university” here in this article. In America, we go to college or go to the university. We will say, when I was at the university, the English will say “when I was at university.” They do the same thing with the word “hospital.” Americans will say, “When I was in the hospital,” but British will say, “When I was in hospital.”
Another good example of vocabulary differences would be that we call the thing you push the baby around in “the baby stroller” or the “baby carriage” in America, but the British push them in a “pram” or a “perambulator.” The front of the car where the motor is located, in America, we say is the “hood,” but in England, it is the “bonnet.” In the back of the car where we put our luggage, in America, we call it the “trunk,” but the British say “the boot.” Switching back and forth in my life from country to country gets me caught sometimes. In America, they say “motor cycle,” but in England, they say “motor bike,” and when my kids hear me say “motor bike” because it comes out naturally without thinking, they laugh at me. There are other vocabulary differences, but these are just a few.
You can even find vocabulary differences when you go from one part of America to another. In most of the United States, when you take the plates off the table after eating, you clear the table. However, in the Ohio Valley, they “rid up” the table. In the south in places like Oklahoma and Texas, one of my favorite dishes is “chicken fried steak.” When I went to the Ohio Valley, I thought they didn’t have it, but I finally learned they have it, but they call it “country fried steak.” I have heard of several differences in vocabulary not just between England and America, but also between the north and the south in America.
Since I began school in England, I struggled with spelling forever. Basically, a lot of the words are spelled the same, but every so often, you can find a word that is spelled differently. An example that I remember specifically being marked by my American teacher when I changed from British schools to American schools was the word “color.” In America, it is “color,” but in England, it is “colour.” There are not many words like that, but every so often, they pop up.
Usually, the British and the Americans understand one another just find when they speak. They are speaking the same language. However, there are some minor differences. These are just some differences that came to mind when I saw they had asked me the question about the differences between British and American English. If someone did an in depth study, they could probably find more, but in general, this explains some basic differences between the way the two countries speak. .