[Roger Slater]

Catherine, a quick Google search tells me GG wrote reviews for the Spectator, but it was the New Statesman whose contest he entered:

Despite his seriousness, Graham Greene greatly enjoyed parody, even of himself. In 1949, when the New Statesman held a contest for parodies of Greene's writing style, he submitted an entry under the pen name "N. Wilkinson" and won second prize. His entry comprised the first two paragraphs of a novel, apparently set in Italy, The Stranger's Hand: An Entertainment. Greene's friend, Mario Soldati, a Piedmontese novelist and film director, believed that it had the makings of a suspense film about Yugoslav spies in postwar Venice. Upon Soldati's prompting, Greene continued writing the story as the basis for a film script. Apparently, however, he lost interest in the project, leaving it as a substantial fragment that was published posthumously in The Graham Greene Film Reader (1993) and No Man's Land (2005). The script for The Stranger's Hand was penned by veteran screenwriter Guy Elmes on the basis of Greene's unfinished story, and cinematically rendered by Soldati. In 1965 Greene again entered a similar New Statesman competition pseudonymously, and won an honourable mention.