Can you tell me the accent of Julie Andrews?

I have come through a range of Hollywood films. And I found many of actors and actresses speak British English with quite different accent than Receive Pronunciation that has been spoken in BBC news.

The example is Julie Andrew in the films: 'the Sound of Music', 'Mary Poppins', and 'the Princess Diaries' as a grandma. And many actors but I can't remember, most of them take a role as a ruling class person. The accent is very clear and easy to comprehend. The RP in BBC is still clearer to me, but the accent gives me a sense of prestige and sound posh.

I wonder whether it is London or Estuary accent or neither, even though I had been in London for a year but cannot tell small differences in accents. I very rarely heard it in TV in British, BBC news, BBC Entertainment channel (International version), and BBC radio online. But It appears quite often in Hollywood films especially films in historical setting of British or European.

Help from a native would be appreciated.

Thank you.

Your answer clear all my doubt. I notice that many actresses in Hollywood films that are over 50 years old always use this accent, classic RP, which I find unfamiliar to my ears. I used to thought that BBC news reporters' accent is the only correct RP. Perhaps, I should listen to some of the British Queen and Tony Blair speeches (They are RP speakers But I never heard them talk), cause I may found some of classic RP characteristics.

That is why I rarely heard it in British TV programme or radio, since the speakers of classic RP suppose to be seniors between 50 and 70 years old.

Your advice is very useful to me. Thank.