The American degree is usually more general. In Britain, you’ll take about 75% or more of your classes in your major (or in support classes for you major like math classes for scientists and engineers). In America, you’ll only be required to take about half your classes in your major. Also, British universities traditionally assume a higher level of knowledge at the start, but the gap has been narrowing as they have changed the secondary school curriculum in Britain. You’ll probably know more about your subject, but much less about other subjects with a British bachelor’s degree than an American one.

Also, note that Scottish degrees are four years, with the first year being to catch students up to the English/Welsh standard, since Scottish students start a year younger. English or Welsh students going to Scotland can usually skip that first year.