Some Parish Records go back to the Twelfth Century but most are from 1538 and until 1837 when it was law for churches to keep records of their parishioners baptisms, marriages and deaths.  With more and more of these records being stored in databases which people can search from anywhere in the world, it becomes more and more likely that most people have an ancestor recorded in them already.  The internet makes it possible for people from all over the world to check to see what their UK ancestors are recorded.