Gillian Lewis (born 1935) is an English character actress who, after a varied stage career in the 1950s and early '60s, appeared in a number of television drama series until the late 1970s. Notable roles were as the runaway heiress Geraldine Melford in the original London production of Slade and Reynolds' musical Free as Air and, on television, as Drusilla Lamb, secretary to Mr. Rose in the detective series of that name.

Gillian Lewis was born in Tisbury, Wiltshire. She trained at the Bristol Old Vic Theatre School and then worked with the company, combining minor acting parts with the job of assistant stage manager. In 1953 she had a supporting role (Cousin Rosie) in Julian Slade and Dorothy Reynolds' Christmas musical The Merry Gentleman at the Theatre Royal, Bristol and the following year worked backstage at the Vaudeville Theatre in London when Slade and Reynolds' Salad Days transferred there from Bristol.

While working with the Ipswich Repertory Company, she met her future husband, the actor Peter Beton (born 1930).

In 1957, after Slade and Reynolds had enjoyed considerable acclaim with Salad Days, Lewis and Patricia Bredin (who in the same year was the United Kingdom's first ever entrant to the Eurovision Song Contest) took the main female roles in their follow-up show, Free as Air, which opened at the Savoy Theatre in London on 6 June 1957 following an initial season in Manchester. Although this and other Slade musicals never quite matched the success of Salad Days, Free as Air, which was set on the fictional Channel Island of Terhou, ran for 417 performances, some critics regarding it as more slick and professional than its predecessor. A cast recording, which includes Lewis singing a solo number, "Nothing But Sea and Sky", duets with John Trevor ("Free as Air" and "I'd Like to Be Like You") and in a trio with Josephine Tewson and Gerald Harper ("Holiday Island"), was released on compact disc in 2007. One admirer has written that her "sometimes uncertain soprano voice" was "tenuous but perched on the edge of beauty". Like Lewis, both Harper and Tewson moved successfully into television in the 1960s. Peter Beton also appeared in Free as Air.

In the early 1960s Lewis played extensively in repertory theatre in Bristol, appearing in, among many other productions, revivals of John Dighton's The Happiest Days of Your Life (1960) (based on his screenplay for the 1949 film starring Alastair Sim and Margaret Rutherford), Noël Coward's Private Lives (1960) and Blithe Spirit (1961) and Oscar Wilde's An Ideal Husband (1960). In 1962 she played the flirtatious Natalia Snevellicci in the Bristol première of Step into the Limelight, a musical by Edgar K. Bruce and Betty Lawrence based on the Crummles theatrical troupe in Charles Dickens' novel Nicholas Nickleby. In 2004 a compact disc was released of "demo" recordings made at the time by members of the cast, with Lawrence on piano, together with ones cut in 1969 when the show was revived in Bristol with a new cast that included Josephine Gordon and Elric Cooper.

Lewis appeared also at other provincial theatres: for example, with Robert Beatty, Kynaston Reeves and Geoffrey Palmer in George Ross and Campbell Singer's Difference of Opinion at the Theatre Royal, Brighton in 1965. She returned to the West End in 1963 for the London première of Leonard Bernstein's On the Town at the Prince of Wales Theatre. In a short run, Lewis took the feisty role of Claire (the part played by Ann Miller in the 1949 film and on Broadway by the show's librettist Betty Comden) alongside two American actresses, Andrea Jaffe and Carol Arthur.

In the mid '60s Gillian Lewis appeared in episodes of such popular television series as Gideon's Way (1964), The Avengers (1965), Mogul (1965), Public Eye (1965) and The Baron (1966). A number of her roles, then and later, were in series that subsequently acquired "cult" status among devotees such as Department S in which she appeared in the 1968 episode One of Our Aircraft is Empty.

In the Avengers episode, "The Man-Eater of Surrey Green" (broadcast December 1965), she played Laura Burford, an old friend of Emma Peel (Diana Rigg) who was mysteriously lured away from scientific work alongside her tactile fiancé to a horticultural project aimed at propagating menacing bean-like plants with gigantic tendrils. As Joyce Grant in The Baron ("So Dark the Night", broadcast 15 March 1967), her father died in a spooky country house just before the series' eponymous hero (Steve Forrest as John Mannering) and his glamorous assistant (Sue Lloyd as Cordelia Winfield) arrived to value some antiques. This was the prelude to "an eerie web of intrigue, murder and revenge, with two girls facing hair-raising danger".