Chalk figures have to be cleaned up fairly regularly to deal with erosion and overgrowth; it seems that the Giant was not always so well-endowed as he is today.  Archaeologist Leslie Grinsell determined that, in the course of one such cleaning-up exercise, the Giant's navel "became incorporated into his private parts, resulting in an upwards extension of between five and six feet"(!)

A Guardian article by Bryan Silcock, from which I learned this (date forgotten) goes on to say: "Grinsell thinks the amalgamation was probably accomplished during a major restoration carried out for Queen Victoria's jubilee in 1887 (her reaction, if any, is not recorded.)  He suggests that it might have been done deliberately by the local inhabitants to provoke their vicar, who had complained of an earlier cleaning that it might corrupt their morals.  He had, according to an account published soon afterwards, "put an end to these scourings".  It seems more likely, however, that the change was simply a mistake.  The vicar's ban could have led to the giant's outline, cut through the turf to expose the chalk underneath, becoming overgrown and difficult to trace precisely."

So far as literary spin-offs go, there's a novel by Penelope Shuttle, The Mirror of the Giant, which is entertaining if frankly bizarre.

Malcolm