Birtwistle himself has no recollection of such an exit and, while he may have disliked the opera, Britten's letters show both sympathy and support for the difficult young composer, and hehelpshim obtain a study fellowship in America.
It's his Trinity College training in London -- he got into composition by applying as a violist, he laughs -- that helpshim go where no classicist likely even knows one might venture.