Denis’s became known in the 1950s and early 60s as a member of Britain’s first ever boy band The King Brothers, one of the most successful pop groups of the era.

He made his break in composing for television with The Adventures of Black Beauty ("Galloping Home"), which won an Ivor Novello Award.He has created themes and incidental music for over two hundred television series including Within These Walls, If It Moves File It, Dick Turpin, Two's Company, Lovejoy, We'll Meet Again and Hannay, as well writing for numerous jingles for radio and television advertising.His film work includes the scores to Simon, Simon (1970), Not Tonight, Darling (1971), Holiday on the Buses (1973), Ghost in the Noonday Sun (1973), Sweeney! (1977), If You Go Down in the Woods Today (1981) and Privates on Parade (1982).

His debut as a theatrical composer was for the original 1977 Royal Shakespeare Theatre's production of Privates On Parade for which he also won an Ivor Novello Award for Best Musical.Other theatre productions include A Saint She Ain't and The Un-American Songbook (with Dick Vosburgh); Stepping Out - The Musical (with Richard Harris and Mary Stewart-David); Bashville and Valentine's Day (with Benny Green); Worzel Gummidge starring Jon Pertwee and Lost Empires (with Keith Waterhouse & Willis Hall); Wind In The Willows and Treasure Island (with Willis Hall); West Five Story (with Richard Harris); Baby On Board (with Mary Stewart-David).

From pop-star to award-winning TV composer and songwriter, Denis has collaborated with such distinguished names as Alan Ayckbourn, Sammy Cahn, Don Black, Tony Bennett, Nina Simone, Peter Sellers, Howard Keel, Sophie Tucker, Lena Horne, Alma Cogan, Albert Finney, Dame Edna Everage, Maureen Lipman, Elaine Stritch, Dudley Moore, Bruce Forsyth, Ronnie Corbett, Judy Garland, Frank Sinatra and even Jimi Hendrix.