His work as an actor, mainly on stage, has included Lark Rise to Candleford at the Finborough Theatre, London, but he has also participated in a number of TV productions and played Dedalus Diggle in Harry Potter and the Philosopher's Stone.
[1] Brett appeared in a 1998 London stage adaptation[2] of Terry Pratchett's Guards!
He also collaborated in writing some of the music and lyrics for the show, along with Antony Burton, John Saxon, Mark Steeves and Ruth Tansey.
In the same year, the Mikron Theatre Company also took the play "Up The Cut" on the national waterways tour, in which he also performed .
In 1980 he appeared in the stage production of The Hitchhiker's Guide to the Galaxy at the Rainbow Theatre as Ford Prefect; although not critically acclaimed, this show was well received by HHGTTG aficionados.