How much of what you remember is true? Like, I spent 30 years cherising Marine Boy as the most fantastic television cartoon series ever, until, err, I actually got some on DVD. And as for that really erie SF movie The Time Travellers which used to turn up on those weekday BBC2 6pm "Sf Season" slots in 1974 or 75, what a huge letdown that was!
Here's one - those fantastic 1970s Brian Aldiss paperback covers Earthworks, Time Space & Nathaniel with those wonderful Bruce Pennington covers.
I'm so sure that, as a schoolboy, I had copies of these in poster form on my bedroom wall - they came free with some comic or magazine. Can't for the life of me remember which one - or did it really happen at all?