Mike Westbrook first made his mark as a composer with his 1960s recordings for Deram,- Celebration, Release and Marching Song, followed by Metropolis for RCA.

Further compositions for Jazz Orchestra include Citadel/Room 315 featuring John Surman, After Smith’s Hotel , the young person’s guide to the jazz orchestra, The Cortege, On Duke's Birthday dedicated to the memory of Duke Ellington, Big Band Rossini which was featured in the 1992 BBC Proms.

Works for classical ensembles include a saxophone concerto Bean Rows and Blues Shots which was commissioned by the Bournemouth Sinfonietta for John Harle, a score for the silent movie Moulin Rouge commissioned by the Matrix Ensemble, and Classical Blues in 2002 for the BBC Concert Orchestra. Mike's television music credits include the award-winning BBC drama Caught on a Train by Stephen Poliakoff  and directed by Peter Duffell starring Peggy Ashcroft and Michael Kitchen.

His involvement in experimental theatre began in the late 60s with the multi-media work Earthrise, and collaborations with The Welfare State Theatre Company and The Cosmic Circus. His work for the stage includes Adrian Mitchell's Tyger a celebration of William Blake, staged by the National Theatre in 1971, and Mitchell’s White Suit  Blues about Mark Twain. His opera Quichotte commissioned by L’Ensemble Justiniana, toured in France in the 1980s. Coming Through Slaughter, based on the novel by Michael Ondaatje about the New Orleans cornettist Buddy Bolden, was premiered in London in a concert version in 1994.

In collaboration with his wife, singer/librettist Kate Westbrook, he has generated a whole series of jazz/cabarets and music-theatre pieces, beginning with the jazz/cabaret Mama Chicago, winner

of the 1978 Edinburgh Festival Fringe Award. This was followed by The Ass, based on the poem by D.H Lawrence, Pierides commissioned by Extemporary Dance Theatre and Good Friday 1663, a TV opera commissioned by Channel Four with libretto by Helen Simpson. Their 2003 composition Art Wolf commissioned by the Aargauer Kunsthaus, Switzerland, is dedicated to the 18th century Alpine painter Caspar Wolf.

Other compositions include two works for voice and acoustic brass, performed by The Village Band,- Waxeywork Show  and English Soup or the Battle of the Classic Trifle which was premiered in 2008. Their 2009 album Fine 'n Yellow was written in memory of friends John and Margery Styles. The Serpent Hit a political fable written for voice, percussion and saxophone quartet, was premiered in London in 2011 at Wilton’s Music Hall. Paintbox Jane, based around the work of the painter Raoul Dufy was performed by Westbrook&Company: three singers, three musicians plus actor Tim Goodwin as Dufy. Mike set Kate Westbrook's texts for her album The Nijinska Chamber a tribute to the dancer/choreographer Bronislava Nijinska,pairing Kate's voice with accordionist Karen Street.  He also wrote the music for Kate Westbrook's Granite Band albums GRANITE inspired by Dartmoor and Earth Felt The Wound, a piece concerned with threats to the environment. He was a member of Kate's Granite Band

The Westbrooks have also created large-scale concert works incorporating settings of European poetry, as in The Cortege a work for voices and jazz orchestra, and London Bridge Is Broken Down for voice, jazz group and chamber orchestra and Chanson Irresponsable for voices, jazz group and string quartet. Westbrook Rossini, variations on themes and arias from the operas of

Gioacchino Rossini began with a small street band in the 1984 Lausanne Theatre Festival. It was later adapted for big band and was later revived under the title Rossini Re-Loaded.  Jago, their first full-scale opera, was commissioned by Wedmore Opera in 2000. Their jazz oratorio Turner in Uri, based on the painter Turner's travels in the Swiss Alps, was premiered in Altdorf and Zurich in 2003. Their opera Cape Gloss - Mathilda's Story for classical soprano and piano, had its first performance at the University of Plymouth in 2007.

Mike Westbrook's albums for ENJA Records include The Cortege, Bar Utopia a big-band cabaret with lyrics by Helen Simpson, The Orchestra of Smith's Academy, compositions recorded ‘live’ by the Mike Westbrook Orchestra and the Steve Martland Band, a tribute to the Beatles Off Abbey Road, and Glad Day settings  of the poetry of William Blake. His releases on the Jazzprint label include Platterback with Westbrook & Company, L'ascenseur/The Lift with The Westbrook Trio, Waxeywork Show with The Village Band and a reissue on CD and DVD of the Westbrooks’ 1980s jazz cabaret Mama Chicago. Reissues on BGO include Citadel/Room 315 and London Bridge is Broken Down, and, on the Swiss label Hatology, On Duke’s Birthday and Westbrook Rossini.

Mike Westbrook returned to big band work with the formation of The Uncommon Orchestra, a 22-piece ensemble based in the South West of England, combining jazz,   rock, pop and classical musicians. The orchestra  released its first album (on ASC Records) A Bigger Show, a ‘jazz/rock oratorio’ with lyrics written and performed by Kate Westbrook with fellow vocalists Martine Waltier and Billy Bottle. Mike also works regularly in The Westbrook Trio with Kate and saxophonist Chris Biscoe. recent performances included a revival of The Westbrook Blake, featuring the voices of Kate Westbrook and Phil Minton in a Choral Version of his settings of the poetry of William Blake.