R.P accent and standard southern English accent

What are the difference between R.P accent and standard southern English accent. Until now, my learning method of pronunciation is by using Oxford dictionary. But recently, I read some tutorials about variation of British English accent. According to that, Oxford dictionary is using R.P English accent and it is old fashioned and not a most using accent. Please any one let me know, if this is true.

Also I have refer Cambridge dictionary. There are some accent difference between these two dictionaries when we look at IPA script with a word's definition. Is Cambridge is standard southern English accent or what ?

Please someone help me to select a dictionary to learn accent, because both dictionaries share same meaning of most words.