If you're under the age of 40 you may never have heard of them, as I believe Double Double Comics were only around from about 1967 to 1970. What were these curious items? Well, in the 1960s unsold copies of American comics were returned to the British distributor, Thorpe & Porter, who repackaged them into giant size "Double Double Comics", so called because they consisted of four individual 32 page comics in one 128 page edition.
The repackaged giants included four full comics, including advertisements and letters pages, but minus their original covers. New covers were bodged together (often having little relation to the stories inside) and the same artwork appeared on the front and rear covers. The interior covers were left blank.
If that wasn't weird enough, the contents of the Double Double Comics could be different even if they had the same cover! It all depended on what spare comics they had to bind together. For example, my copy of Action Double Double Comics includes Action Comics Nos.342, 344, and 348 plus Showcase No.63, but someone else's copy (as reported here) includes Action Comics Nos.342, 343, GI Combat No.117 and Inferior Five No.2.
Each Double Double Comic usually bound four DC Comics together, but I remember that sometimes the occasional Marvel title was included too. (I recall a Gene Colan Daredevil in one issue, alongside three DC Comics.) The drawback was that you might already have one or two of the comics in the selection, or there might be one comic in there you didn't like. Basically it was pot luck, but we couldn't complain. Back then four American comics would cost a shilling (5p) each but Double Double Comics were only 1/9d (9p).
Marvel UK tried a similar idea in the late 1970s with three softback books that bound together several unsold weekly comics, including their covers. However it's the Double Double Comics that seem to have become quite collectible. (Speaking of which, and vested interest declared, I currently have a couple up on eBay here and here if you're interested.)
I'm not sure how well the Double Double Comics sold in the 1960s. Perhaps repackaging the comics was more trouble than it was worth. They were nice value for money books though, and I'm surprised more publishers haven't attempted something similar in recent times.
