1. Pronunciation: British English is usually pronounced clearly and accurately, while American English is pronounced casually and naturally. In British English, the sound "R" is usually pronounced clearly, while in American English, the sound "R" is often omitted.

2. Expression: British English is usually more formal and precise, while American English pays more attention to colloquialism and conciseness. In British English, the police will say "Iarrestyou", while in American English, they will say "You're Reunderrarrest".