Here is more info on it: Zenopus Archives - The Dungeons of the Ground Goblins
"It also turns up occasionally with OD&D boxed sets in the UK. "

Is the quote above from the Zenopus site a typo? I had always heard that it was included with the Basic Set, but it seems plausible that it might have been included in GW-distributed copies of OD&D as well.

The page you reproduced is not on the Zenopus site. Is it a different edition, or are the pages shown on the Zenopus site different parts of the edition you have?

aia wrote in GW leaflet: The one on the site seems white...

So yours corresponds to:

'4th: Games Workshop flier, ~Dec 1977, front shows UK Basic Set (see right) A similar flier but with different artwork. The title returns to "DUNGEONS & DRAGONS", but with the same subtitle as above,' ['above' meaning the 3rd version, described below, per the multiversal principle 'as above, so below']

from the Zenopus site, & not

'3rd: Games Workshop flier, ~Feb 1977, front shows OD&D booklets (see right) Here it is titled, "VISIT A WORLD OF SWORDS & SORCERY With DUNGEONS & DRAGONS" and subtitled "DUNGEONS & DRAGONS is the ORIGINAL Adventure Game in Worlds of the Strange and Fantastic" '

?

Speaking of different versions of the leaflet, i believe this OCE has the TSR version included (along with a holmes dice set!):


** expired/removed eBay auction **

Ok, in order to have a complete view, i created a "medley" of the 4 pages of the leaftlet... the order of the pages is the one presented in the sequence.
And yes, i do confirm that it is an A4 sheet bent in two: it fits an OCE without any problem!