In 1973 Bentley wrote the book and lyrics for Shylock, a musical version of The Merchant of Venice, performed at the 1974 Edinburgh Festival.

[4] In 1977 an updated version called Fire Angel,[5] set in a 20th century New York City Mafia nightclub, appeared at Her Majesty's Theatre, London.

[11] This success led to four back-to-back West End shows lasting five years: Lend Me A Tenor, Follies, Cats and Aspects of Love.

Next came an off-West-End Assassins followed by a national tour of Aspects of Love,[12] then Phantom of the Opera in Manchester[13] and back to London for Company, Kiss Me Kate and Dame Edna – the Spectacle.

In 1994 Bentley was asked by the Danish composer Poul Ruders to write the libretto for his opera The Handmaid's Tale based on Margaret Atwood's novel,[15] which won a Cannes Classical Award and Reumert Prize.

[19][20] Librettos for three other composers followed: Ana Sokolovic's The Midnight Court,[21] Dominique Le Gendre's Bird of Night[22] and James Rolfe's Inês.

[23] Bentley has also written a novel, The Man Who Came After Hyacinth Bobo, about the Fourth Crusade and the Siege of Constantinople, published in Greek[24] and English,[25] plus occasional newspaper and magazine articles.

[26] Bentley took part in Mastermind on BBC TV (15 March 1992) where his specialist subject was The Life and Works of King Ludwig II of Bavaria.