There are many differences between American and England's pronounciation. Just as there are many differences within each society. Someone from Texas sounds different than the people in New York, as do people from different parts of London.
Some brief examples that are well known.
Tomato England, the a sound is like ma, as in your mother
Tomato American, the a sound is the long a as in the month of May
The same goes for potato.
The a sound is typically different, take the word can or can't, in American English the a is like ant the small insect, whereas in England it would be like your aunt.
Note that in America, your ant and your aunt may be pronounced the same or may be said with the more British sound, more of a ou sound.
This subject is really a tough one for writing, as I don't like Phonetics. They didn't teach that way when I was coming up.