There have been a few times over the past 10 years or so when, feeling as grey as London skies and walking with eyes down to the pavement, I’ve spotted a hard little dazzle of primary colour and felt immediately cheered. Those little spots of intricate brightness are the work of the city’s “chewing gum artist” Ben Wilson, who, since 2004, has spent most days painting whimsical miniatures on some of the millions of flattened blobs of gum that are spat out on the city’s paving stones. Each of Wilson’s paintings is unique; most are dedicated to passersby who ask him to celebrate friendships, or to memorialise lost loves, or…