1982, J. C. Wells, Accents of English 2: The British Isles, Cambridge University Press, →ISBN, page 331:
Awareness of the fact that Yod Coalescence is somewhat stigmatized leads to hypercorrection in would-be elegant speech, with the use of [tj, dj] in place of [tʃ, dʒ] in words such as chew, June.
In this investigation, the linguistic context is restricted to /j/ after /t, d/ in stressed syllables within a word (e.g. tune, duke). This is the environment in which Yod Coalescence is not (yet) fully acceptable within RP.