|THE LETTER -R-|
This is probably the most important difference between BrE and AmE, or at least the easiest to detect.
In British English (Uk, Australia, Caribbean, etc.) the letter R is only pronounced when followed by a vowel. In American English (the USA and Canada), people pronounce this letter always.
teacher /ti:tʃə/ /ti:tʃər/
In BrE a final -R is silent, because it is not followed by a vowel, so TEACHER is pronounced /ti:tʃə/. But if that word is followed by another word that begins with a vowel, then the R is followed by a vowel and so, it is pronounced:
He's the new teacher of maths now, the final -R in TEACHER is pronounced "teacherofmaths": /hi:z ðə nju: ti:tʃər əv mæθs/
This final R that joins one word with the next is called a "linking R".
In BrE, words ending in R sometimes pronounce it (linking R) and sometimes don't pronounce it. From a native's point of view, there are words that end in a vowel but when the next word begins with a vowel they use an / r / to join both words. Then, it is only natural that sometimes they use a "linking R" in the wrong place. We call that an "intrusive R", and it happens a lot in BrE.
A book about Africa and America many British people will pronounce this "africarandamerica"
The sound / r / has usually changed the pronunciations of the previous vowel. This is the table of changes that explain the present pronunciation of many words:
|without r||can||pen||bid||stop||cup||feel||mean||took / food||house||day|
|with r||car||person||bird||fork||purse||beer||bear / fear||door||hour||pair|
In all these examples with R, AmE pronounces the R and BrE doesn't, but both of them present the same change in the vowel before the R. So this letter, silent or not, is marking a change in the previous vowel.
EXCEPTIONS TO THE GENERAL RULE
Standard American English, as we said, always pronounces de R, whether or not followed by a vowel. But some local dialects follow the British rule and only pronounce it when followed by a vowel. For example in the state of New York the R follows the British usage, although this trait is declining and mainly surviving in rural areas.
Most importantly we must refer to the American black pronunciation. Black Americans (or Afroamericans) also follow the British usage in this, although part of them uses now a standard pronunciation. The biggest impact of this is through songs. Black Americans are now leading music styles such as hip-hop, rhythm & blues, gospel, jazz and also have a good share of pop hits. As a result, their pronunciation is now being imitated by white singers too, so you can find many American singers of any race following the British rule for the R when singing, even if they follow the American rule when they are speaking. British pop may also have influenced this pronunciation. The reason is that singing this way sounds "more cool" and fashionable in those specific contexts. Latino population in some parts of the States is also under the black American accent influence, probably because in many areas they live in the same districts.
Example: This American band is following the British rule, so they do not pronounce the R except when followed by a vowel; check it out: Mirrors (by Boyce Avenue)
Also, you can find many people pronouncing the R "the American way" -that is, always- in the North of England, Ireland and Scotland. Only the southern dialects lost the R when not followed by a vowel, but the same thing did not happen in the rest of Britain. Nevertheless, the influence of the standard pronunciacion caused most educated people all over the country to drop their Rs too, but still you can find many others who still pronounce it, especially if they keep their dialectal accent.
In conclusion, you can find American people following the British rule for the R, and British people following "the American" rule, but for most of the population, the general rule is true: Americans always pronounce the R, British English speakers (in Great Britain, Australia, New Zealand, South Africa, the Caribbean etc) only pronounce the R when followed by a vowel.