SOUND Focus:

  LINKING R

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".

  INTRUSIVE R

In Brititsh English, 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"