Still getting nowhere with this: Which British actor said to a successful TV and Film actor 'You're doing it the wrong way round, my boy.You're a star and you don't know how to act. Laurence Olivier has been suggested to Dustin Hoffman when making Marathon Man, but the quote is not exact and I can't see DH being described as a TV actor first.
only thing i could find is the following quote from Laurence Olivier
"Dear boy, it's called acting." - upon seeing Dustin Hoffman's "method" acting by not sleeping and making a mess of himself to get into character while shooting "Marathon Man".