Just for the sake of this having an answer that's an answer, rather than a comment...
As StoneyB and P. E Dant Jun note in the comments, it is a pun on a Browning quotation, "Oh, the little more, and how much it is! / And the little less, and what worlds away!", but with "more" replaced with "Moor". Nowadays, "moor" is almost always a term for a sort of rough upland we have a lot of in Britain, but capitalised it's a now largely obsolete demonym for people of a certain ethnicity. Or several ethnicities. Sometimes we were a little confused about that.
Anyway, it's an ethnic identification that was closely associated with Morocco. Maybe the similarity of name isn't a coincidence, and maybe it is but that led to the closer association. Really, it mostly referred to the multiple ethnicities of Muslim who conquered and held what's now Spain and Portugal for quite some time (hence references in history to "Moorish Spain").
Hence the humour. To be educated for much of British history largely consisted of being forced to study a certain accepted canon of texts, both classical and comparatively modern. So educated men would be expected to get the Browning reference.