Found this poster here. It seems this was a genuine Hammer film that just never got made.
The poster was put together to interest potential investors. The story was to have been similar to The Land That Time Forgot (but this time with a Zeppelin) A Zeppelin on a bombing raid over England is blown of course and winds up at some sort of Lost Continent. More chit chat about this film here. Of on a tangent here but did not realise that Michael Moorcock was one of the Screen Writers for The Land That Time Forgot.