Bacall Perhaps Found Fact Reflecting Fiction When Mathews Was Photographed by a National Newspaper in the "Star" Dressing Room

Sheila Mathews, a West End musical performer who became an early star of ITV when it launched in 1955, has died aged 99. She went on to take straight acting roles and in 2017, at 90, was recognised by the actors' union Equity as the country's longest-running performer. She was only three when she made her stage debut in her dance school's troupe the Rosebuds at Alexandra Palace, London, in 1930. "I was pushed on in white satin pyjamas and sang Close Your Eyes," she said. At 16, her dancing partner was Eric Bartholomew (later Eric Morecambe) at the Prince of Wales theatre in the wartime revue Strike a New Note (1943), a showcase for new talent notable for launching the career of the comedian Sid Field.

A year later, she appeared wearing top hat and tails alongside Tommy Trinder in the musical Happy and Glorious at the London Palladium, and she returned there in 1950 in the revue Out of This World, starring Frankie Howerd, to take roles billed as the Goddess of Happiness and the Vamp. While she was performing in cabaret in the US (1951-55), where television was taking off, her agent told her: "See all the shows you can and pick up all the tips you can. It paid dividends when she returned to Britain for the start of ITV, Britain's first commercial channel.

She appeared in two of its opening Gala Night programmes: Channel Nine, introducing viewers to some of the performers they would see in ITV's forthcoming variety series, and Star Cabaret. A day later, she launched her 10-minute weekend show, Friday's Girl (1955-56). "In this unsophisticated, informal programme, Sheila Mathews will sing three songs of varying types – bright, point and ballad – accompanied by an ensemble of piano, bass, drum, vibraphone, electric guitar and clarinet, explained TV Times magazine.

She often phoned viewers for their requests. In 1957, she married the programme's director, Charles Reading, known as "Mr Palladium" for the eight years he had spent at the London theatre as a stage designer and adviser to the impresario Val Parnell. Reading also guided her career, which continued as a presenter of "ad-mags" (extended, magazine-style commercials, usually featuring household products) such as On View and Quick on the Draw, until they were banned in 1963 for blurring the line between advertising and programmes.

At the same time, Mathews appeared in Scottish Television's popular regional lunchtime variety show The One O'Clock Gang (from 1957 to 1961) and the first series of Southern Television's late-night revue Sweet 'N' Sour (1961), starring Clement Freud. As Mathews's West End musical theatre career continued, she understudied Anna Neagle as Lady Hadwell, the aristocrat's widow, in Charlie Girl (Adelphi, 1965-71), taking over the role for several weeks in 1968 when Neagle was ill. She was also the understudy to the American star Lauren Bacall in Applause (Her Majesty's theatre, 1972-73), a musical adapted from the 1950 film All About Eve.

When Bacall, fresh from the Broadway production, took a holiday during the London run, Mathews stepped in to play Margo Channing, an ageing star taking under her wing a fledgling actor who tries to steal her career and her partner. Bacall perhaps found fact reflecting fiction when Mathews was photographed by a national newspaper in the "star" dressing room. She is said to have stormed back early from her break and told Mathews: Honey, you just played your last show.

When straight acting opportunities came her way, Mathews jumped at the chance to play Laura Marshall, a teacher who became engaged to the motel manager David Hunter (played by Ronald Allen) in the ITV soap Crossroads in 1974. In the event, Laura called off their engagement when David's ex-girlfriend and secretary returned. Despite his assurances, she refused to believe that he still had no feelings for his former love. Born in Edmonton, Middlesex, Sheila was the elder daughter of Reta (nee Adamson) and Walter Mathews, a bank clerk.

A singing coach, Marion Brown, spotted her in a song-and-dance production and offered free tuition. As a child, she was also in films, mostly in crowd scenes, but did play Charles Laughton's daughter in the 1936 biopic Rembrandt. She was a performer and presenter in the early days of ITV and a stalwart of West End musical theatre.