It's not big and it's not clever

As a Yank who does the Guardian crossword, I often come across words or phrases that are common in the UK, but rare in the US. The current case is "It's not big and it's not clever." I've googled it, and found many examples of usage (including a disturbing recommendation about a dwarf), but I would like to know where it comes from, and its original context.

How many letters?