a- Letters from a Life: Selected Letters and Diaries of Benjamin Britten, Vol. 1, Letter 10 [to his mother]

In [b], Schafer asked Britten if he was a PP possessor, to which Britten replied that he did have it, but it seemed to have "slipped a bit", i.e. he now tended to hear a piece in C Major in "his" C sharp, which seems to tie in with a remark one of your other respondents made [e.g. Richard Rodney Bennett, Alicia De Larrocha, Mike Renzi, Sviatoslav Richter - Ed.]