Hulke's main writing partnership was with Eric Paice; their first TV play was a 1958 piece about an IRA man on the run starring Patrick McGoohan. They then wrote four TV SF series, Target Luna, Pathfinders in Space, Pathfinders to Mars and Pathfinders to Venus in 1960-61; I haven't checked to see if any of that survives. Hulke then wrote nine episodes of The Avengers, four of them with his lodger, one Terrance Dicks, who then brought him into Doctor Who. He later wrote seven episodes of Crossroads and several spinoff novels for that series. In non-fiction, he wrote most of the first edition of The Making of Doctor Who and a very good book on Writing for Television which I read many years ago.
Herbert makes the obvious point about the general compassionate approach and specifically anti-authoritarian streak of Hulke's Doctor Who work, but it's a shame that he didn't also look for this theme in, say, his Avengers scripts or indeed the earlier Pathfinders work. (I suspect that the Crossroads material may be less promising in that regard.) I'm also still intrigued by his apparent obsession with reptiles. Still, I am very grateful to Andrew M. Butler for getting this for me from the publisher.