As an actor, his most famous television role was that of Paul Collier in the long-running Doctor sitcoms, beginning with Doctor in the House in 1969. He began contributing scripts to the series during its first sequel Doctor at Large (1971) and continued in the dual role of actor and writer throughout Doctor in Charge (1972-73). Subsequently, he opted out of appearing in any more sequels, but continued to write for Doctor at Sea (1974) and Doctor on the Go (1975). In 1991, Layton resurrected the original characters for a reunion series entitled Doctor at the Top and again wrote scripts and played Collier.
Away from the Doctor series, Layton wrote episodes of numerous sitcoms, including Nearest and Dearest, On the Buses, Romany Jones, My Name is Harry Worth, My Brother's Keeper (in which he also starred), Robin's Nest and Me and My Girl. He also created and wrote two original hit sitcoms for the BBC: Don't Wait Up (1983-90) starring Nigel Havers, and Executive Stress (1986-88) featuring Geoffrey Palmer.
Other television appearances include: Z Cars, The Likely Lads, United!, Doctor Who, Jackanory, The Liver Birds, That's Life!, It Ain't Half Hot Mum, The Sweeney, Minder, Sunburn (opposite Michelle Collins), Doctors, Holby City, Heartbeat, The Bill and, most recently, Norman Simmonds in EastEnders. He was also the voice of Sydney in the long-running series of commercials for Tetley tea.
His film credits include: Here We Go Round the Mulberry Bush, Carry on Behind, Confessions of a Driving Instructor, Stand Up, Virgin Soldiers and Don't Go Breaking My Heart.
On stage, he has appeared in numerous productions, including Billy Liar (King's Head, Islington) alongside Sherrie Hewson and Rebecca Callard, while in the West End, he performed in Chicago (Adelphi Theatre) and as Fagin in Oliver! (London Palladium).
A published author, his books The Swap and Other Stories, The Fib and Other Stories and The Trick and Other Stories have been included on the National Curriculum for schools.