She was the ideal collaborator with Benjamin Britten to provide for him the librettos of three of his operas, as she could convey the unease of the disturbing stories that he chose, while allowing space for the music he would write. She understood what his musical imagination needed, just as in the 1930s she had responded to the new abstract painting of Mondrian and Kandinsky in Paris, and had promoted them and the young British avant-garde by founding and editing the magazine Axis. Her marriage to John Piper for more than 50 years was a close duet of writer and painter, in which their house in the Chilterns where they lived from 1935 became a creative centre for the collaborative arts.
Myfanwy Evans was born in 1911 in London, the only child of a Welsh father and an English mother of Huguenot origin. Both her grandfathers were ministers, one Welsh-speaking in Tenby, and the other, Charles Playll, a Congregational Minister at Louth. Her father David Evans was a dispensing chemist, and she grew up in his house over the shop Allchins in Englands Lane, Hampstead. It was the inspiring teaching at North London Collegiate School that introduced her to the arts, and enabled her to win an Exhibition to St Hugh's, Oxford, in 1930.
Women at Oxford were then still merely a part of the background, but she was an outstanding swimmer, and captain of the team that won the university match in 1932. Her interest in modern art and literature was encouraged by her friendship with her contemporaries Justin Blanco-White, the future architect, and Nicolete Binyon. It was through Justin's parents that she met the painter Ivon Hitchens, who invited her to join a summer painting party at Sizewell in Suffolk in July 1934. One of the artists was John Piper, who had recently separated from his wife. He and Myfanwy were an instant success with each other, enjoying different styles of upbringing, an eight-year-old difference in age and complementary interests in modern art as admirer and practitioner. They married in 1937.
She had already arranged to spend four weeks in Paris, and Piper put her in contact with the French-American abstract painter Jean Helion. It was a crash course in modernism, making appointments and visiting studios, at a unique time when there was developing a new taste that was determined to be international, yet still only appealed to a tiny number of intellectually lively people. Helion encouraged her to found an English review of abstract art, and recommended her to Ben Nicholson, the leader of the group in London.
Axis was published from 1935 to 1937, and is remarkable first for her confidence in selecting worthy contributors as writers and artists, and second for a gradual shift in taste, towards rebuilding an English primitive tradition on abstract principles, evident as much in her own editorials as in John Piper's painting.
She and John moved into the abandoned farmhouse at Fawley Bottom, beyond Henley, at first with no water, electricity or heating. Only slowly becoming less uncomfortable, it nevertheless became the focus of a group of friends, especially John and Penelope Betjeman, Geoffrey Grigson, and Osbert and Karen Lancaster. Betjeman so adored Myfanwy that he wrote poems about her in the totally imaginary character of a nanny, and as an undergraduate, equally unlike, at Oxford.
As her husband John began to work regularly with publishers and for public commissions, her role as artist's assistant became more demanding, and writing in any case took second place while their four children were young. The house became a refuge during the war, often for John's patron Kenneth Clark and his family. Clark commissioned from her a Penguin Modern Painters volume on Frances Hodgkins, which remains one of the most convincing appreciations of a modern British painter.
She had known Britten from the time of a notably argumentative meeting of the Group Theatre at Fawley Bottom before the war. They became much closer while John was designing for him and was a Director of the English Opera Group. They heard all his new music, and Britten in turn looked up to John as a mentor in modern art. The Pipers lived so far from Aldeburgh, were not part of Britten's immediate circle, and could not become, even potentially, rivals, that they were among the few who remained his lifelong friends.
It was Myfanwy who suggested that Henry James's The Turn of the Screw would appeal to him as a situation for an opera, and they at first worked together on it, informally, until the commission from La Fenice in Venice was arranged in 1953. Problems of simplifying the plot were solved by setting it as a series of linked scenes, to be designed by John. The precise meaning of the haunting and the corruption of the children was hidden by use of poetic language, and Myfanwy was able to half-conceal and half- reveal the sexual implications, leaving much open to the music and the performance.
The friendship with Britten was later strained briefly by her and John's support for the South African dancer and choreographer John Cranko, who Britten at first accepted, but then dismissed. For Cranko's friend the Danish actor Erik Mork, she re-cast as a play Kierkegaard's novel The Diary of a Seducer.
The proposal to use another short story by Henry James, "Owen Wingrave", came from Britten, and Myfanwy adapted this pacifist dilemma as an opera for BBC television. They worked together again, before the first broadcast of Owen Wingrave in 1971, on Britten's last choice, Thomas Mann's novel Death in Venice, beginning it during a driving holiday in France with Peter Pears and John. This complex plot was reduced to scale by allocating all the roles of tempter to a single character, and the complexity was then given back to the music by a setting at multiple levels of reality, including a counter-tenor part as Apollo, and a Pentathlon, at one time planned to be acted nude. Myfanwy recently completed an opera after Strindberg's Easter, working with Malcolm Williamson.
It is remarkable how few direct portraits John made of Myfanwy, but how many indirect. These include countless life drawings, which were the foundation of some of his paintings, and conclude with photographs published as screenprints. Her practical gifts to John's art are evident, but far more important was her equal contribution to their exceptional evolution into what Kenneth Clark described as "two of the most completely humanised people I have ever known". Fawley Bottom was a model of hard work and friendship. Myfanwy was renowned as a pioneer of a French style of cooking (first learnt from Boulestin). They gave memorable parties, often with fireworks, in which the house was turned into an enchanted stage set. Since John delighted in working with other artists and specialists, the use of his house as an extensive workplace was vital.
In her last years she endured the loss of her eldest child, the artist Edward Piper, and devoted more care than seemed possible to looking after her husband John in his slow decline until his death in 1992.
Mary Myfanwy Evans, art critic and librettist: born London 28 March 1911; married 1937 John Piper (died 1992; one son, two daughters, and one son deceased); died Fawley Bottom, Buckinghamshire 18 January 1997.