For many decades the voice of British science fiction, New Worlds varied from being a fan-zine to a professional periodical to a series of paperbacks. It is perhaps most famous today for being the main publication for the British “new wave” of writers: J.G. Ballard, Michael Moorcock, Brian Aldiss, etc.
Published from 1946 through 1979 (re-emerging for sporadic public in the 1990s), New Worlds provides a fascinating source for cover artwork. All the following images come from The Visual Index of Science Fiction Cover art, which hosts a variety of exciting SF artwork. Their New Worlds page is here and their main page is here. Enjoy.