As I'm about to revise a blog entry of mine (see here) I'm currently giving some books a close reading again. One of them is A.C. Gimson's An Introduction to the Pronunciation of English in its various editions.
The first and second editions first appeared in 1962 and 1970 respectively. They comprised eleven chapters. Ch. 11 bears the title "The Word in Connected Speech" and deals, among other things, with weak forms, elision, liaison. With the appearance of the 3rd edition a twelfth chapter of about 27 pages length was added: "Teaching the Pronunciation of English". Inter alia Gimson writes about the "Choice of Models of Pronunciation". Homing in on the foreign learner and the choice of a basic model for him he points out that RP should be regarded as an evolving mode of pronunciation. Due to the fact that there has been a "considerable dilution in the original concept of the RP speaker" 302), Gimson advises the foreign learner to strive for the "educated speech of the South East of England" (302). And then he makes an almost 'heretical' remark:
"It can of course be claimed that the traditional concept of RP suffers such dilution as a result of the tolerances suggested that a new label should be applied to the model. 'General British' (GB) has been used1 and may supersede the abbreviation RP." (303)
But then, the thought of giving up RP as a label seemed to have been too daring to him, so he (hastily) adds this sentence: "But so widespread in Britain and abroad is the use of the term RP that it is retained in this discussion." (303) ... Phew! Escaped by the skin of his teeth!