For the libretto, Slater eschewed the traditional five-stress line form of English rhyming or blank verse in favour of a more modern and conversational four stress line with rhyming couplets. He argued that contemporary listeners were accustomed to assonance and consonantal rhyme but it could also be argued that this form of 'rough' rhyme was common in early English drama and that Slater was restoring it to the stage, rather than inventing something new. Slater's original libretto, which he published himself (to the annoyance of Britten and Peter Pears, who had made a number of amendments to it before the opera was staged), is cast in three acts. It omits the repetitions necessary in the actual opera.
Slater was involved, with Britten and W. H. Auden, in many of the John Grierson documentaries, such as Coal Face. He wrote the scripts for several films, including The Brave Don't Cry (1952), about a mining disaster. Britten dedicated his Temporal Variations for oboe and piano to Slater, and his Ballad of Heroes to Slater and his wife Enid.
The literary papers and correspondence of Montagu Slater are held at The University of Nottingham.