The name was definitely ringing a bell with me, and I was raised 220 miles from Hendon and never went anywhere near a Butlins camp.
A Google search on the term "Boko" reveals that it seems to be a Moslem given name (cf: Abdul, Hassan, Ali, etc). But I didn't find what the farthest reaches of my mind were suggesting.
Then I remembered that the words "big" and "fat" seemed linked with "Boko" and a search on "Big Fat Boko" found... well... Big Fat Boko (a wizard in a comic strip, as I had partly-remembered). He was a character in The Topper, which, along with stablemate The Beezer, was a rival to DC Thomson's Dandy and Beano in the 1950s.
http://petergraycartoonsandcomics.blogspot.co.uk/2008/07/ken-hunters-comic-big-fat-boko.htmlJN