During the demo, Sellars decided to make a career, appeared with Lionel Westlake’s company on a tour of The Hasty Heart in 1947, then became a representative as an assistant stage manager and actor in Grange-over-Sands. .
After a season at St Anne’s he made extensive tours to Derby – where he began directing plays and where John Osborne was a member of the company – and to Northampton.
In 1958, Sellars joined the BBC as a stage manager on programs such as Quatermass and the Pit (1958-59), then became a production assistant. Working on another sci-fi soap opera, A for Andromeda (1961), he had the challenge of encouraging a nervous Julie Christie, straight out of drama school, to speak less quickly.
He made uncredited appearances in that sequel and the following year, The Andromeda Breakthrough.
Raised to the rank of program director, Sellars worked on a series of soap operas – Compact (1965), 199 Park Lane (1965), the United football series! (1965-66) and The Newcomers (1966-67).
In 1967, he became producer of The Newcomers, in which his wife, actress June Bland, whom he married in 1950, played Vera Harker.
The soap opera – set in the fictional overflow fictional East Anglian town of Angleton – had started two years earlier, with Verity Lambert at the helm. He was its fourth producer, directing nearly 300 episodes until its completion in 1969.