The production team changed during the series' long run, particularly between the third and fourth series, but the influence of Brian Clemens was felt throughout. He wrote the second episode and became the series' most prolific scriptwriter. Succeeding producers Leonard White and John Bryce, Julian Wintle became the producer of the 4th series with Brian Clemens credited as associate producer and Albert Fennell credited as "In charge of production". For series 5, made by A.B.C. Television Films (which was created during the run-up to Associated British Corporation and Associated-Redifussion forming Thames TV) Clemens and Fennell became co-producers, with Wintle as executive producer. For series 6, after its initial producer John Bryce left, Clemens and Fennell returned as co-producers; early episodes also credit Julian Wintle as consultant to the series and Philip Levene as story consultant.