IN A remarkable theatrical family Mary Hayley Bell tended to be overshadowed by her husband, John Mills, and their daughters, Juliet and Hayley. Yet while she was happy to fulfil the traditional roles of wife and mother, and did so with unswerving loyalty and affection, she managed a not inconsiderable career of her own.

She had started in the theatre as an actress but became better known for writing plays than appearing in them. She was nothing if not prolific. Working from a caravan at the bottom of the garden at the family home in Richmond, Surrey, at one time she was turning out a play a year.

Not all reached the West End and some were not even accepted for production. Among the disappointments, however, were tangible successes, especially when her husband was the leading man. He starred in Men in Shadow (1942), Duet for Two Hands gave him a long London run in 1945 and eight years later he was with Joan Greenwood in The Uninvited Guest, an excursion into Victorian madness which required him to sport a blazing red wig.

She continued to write plays until the early 1960s when, after her latest effort had been rejected, she decided that the theatre no longer wanted her. In the meantime, however, she had turned to writing novels. Her most notable book was Whistle Down the Wind (1958), the story of three children who mistake an escaped murderer for Jesus Christ. It was sensitively filmed in 1961 by Richard Attenborough (as producer) and Bryan Forbes (as director) with the location changed from the Home Counties to Lancashire. Hayley Mills gave a fine performance in the lead role.

Many years later Whistle Down the Wind was turned into a stage musical by Andrew Lloyd Webber, still set in the 1950s, but relocated to the American Deep South. The show had a chequered history. It opened in Washington to mixed reviews, a New York transfer was delayed and then cancelled, and a smaller, cheaper production eventually opened in London in the summer of 1998.

Bell was not involved in either adaptation of Whistle Down the Wind but she was co-writer of the 1965 film Sky West and Crooked. This was a family affair, with John Mills directing and Hayley starring as the retarded girl who falls in love with a gypsy, played by Ian McShane.

Mary Hayley Bell was born in Shanghai and spent a colourful childhood in China where her father was a customs official. Originally put in the charge of a governess, she later went to school in England, attending Malvern Girls’ College and excelling at lacrosse.

When her father lost his money in misguided Far Eastern ventures she had to fend for herself, and set out to become an actress, studying at the Royal Academy of Dramatic Art. She made her first stage appearance in 1932 in Shanghai, playing Henrietta in The Barretts of Wimpole Street with an American touring company.

She had her first London part two years later. There followed a series of plays in the West End, a tour of Australia with Fay Compton and a New York debut in 1939. She gave up acting on marriage, and did not return to the stage until the mid-1950s when she and Mills toured British Army camps in Germany in Agatha Christie’s whodunnit, The Mousetrap.

She first met Mills in the 1930s when he was touring the Far East. Some years later they met again in London at a painful time in both their lives. His first marriage had ended and she had been jilted by her fiancé.

They married at Caxton Hall register office in January 1941 and it proved to be one of the longest, closest and happiest of showbusiness unions.

Bell obeyed the convention of the time that on marriage women should put aside their own careers and concentrate on raising the family. She and Mills had three children, a son, Jonathan, as well as Hayley and Juliet, and Bell did her best to keep a maternal eye on them, not least when Hayley became an international child star at the age of only 14.

Writing provided a welcome diversion from family duties, though Bell lived very much in her husband’s shadow. In the 1960s she was appointed a magistrate but was asked to resign three years later because it was felt that she was spending too much time with Mills while he was abroad filming. She did not hide her disappointment.

In 1968 she brought out an autobiography, What Shall We Do Tomorrow? and in 1981 produced a book about the family dog, a Yorkshire terrier called Mr Chips.

Her later years were difficult ones for Bell. She lost her sight, suffered from Alzheimer’s disease and was latterly confined to a wheelchair. But in January 2001 she was able to walk up the aisle with Mills when they renewed their wedding vows on their diamond anniversary.

Sir John Mills died in April, aged 97, and she is survived by her children.

Mary Hayley Bell, actress, playwright and novelist, was born on January 22, 1914. She died on December 1, 2005, aged 91.