I know little about John Keay and what is known is confused by the fact that there have been two artists by the same name. I think - but I'm not 100% sure - that the artist who contributed to Fontana was known as Jack Keay but was born John Edwin Keay in Kings Norton in 1907 and died in London in 1996. He was represented by Linden Artists and Thomson Artists.
Then there was a second artist by the name of John R. Keay represented by John Martin & Artists who did various series for Look and Learn in the late 1970s, his work often to be found on the inside front cover on series like 'This Made Headlines' and 'Dateline'.
If anyone has any further information that might help me separate out the two, please let me know. In the meantime, here are a few of Jack Keay's covers for you to enjoy.
Fontana Books 439, 1960
Fontana Books 621, 1961
Fontana Books 629, 1962
Fontana Books 658, 1962