Publisher:Mayflower-Dell

1960s imprint of Mayflower

Addresses:

 * 1963: "Mayflower-Dell Paperbacks are published by Mayflower Books Ltd, 282 Vauxhall Bridge Road, London S.W.1" Source:
 * 1964 - Aug 1965: "Mayflower-Dell Paperbacks are published by Mayflower Books Ltd, 319 High Holborn, London W.C.1"
 * Oct 1965 - 1967: "Mayflower-Dell Paperbacks are published by Mayflower Books Ltd, Kingsbourne House, 229-231 High Holborn, London W.C.1"

The Best of Sci-Fi Series
Mayflower-Dell ran a series of Anthologies that don't exactly match any US series: One and Two are listed as being by Judith Merril but there's yet no telling which books they're based on.
 * Three is "Great Science Fiction Stories" for various years.
 * Four is "The 8th Annual of the Year's Best S-F" for 1962.
 * Five is "The 5th Annual of the Year's Best S-F" for 1959.

The series goes from Best of Sci-Fi Five straight onto 9th Annual S-F, 10th Annual S-F etc.