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"
This flier was produced for Games Day 2 (Feb 12, 1977) and is reported to have been distributed by Games Workshop with price lists or sample copies of Owl & Weasel (the precursor to White Dwarf magazine). It also turns up occasionally with OD&D boxed sets in the UK.
The cover uses images & text (except for the box at the bottom with the Games Workshop address) from an earlier TSR advertisement, shown here on the Playing at the World blog.
The interior uses TSR D&D artwork from the covers of Underworld & Wilderness Adventures and Supplement I: Greyhawk. At the time, Games Workshop was starting to publish licensed UK versions of TSR material (e.g., UK Holmes Basic set, published in 1977-78), which gives this sample dungeon quasi-official status.