He made twelve appearances at the IAAF World Cross Country Championships from 1977 to 1995. Individually, his performance came at the 1983 IAAF World Cross Country Championships, where he placed seventh overall. Clarke was a three-time silver medallist at the competition (1982, 1987, 1989) and also won a team bronze in 1992, sharing the honours with Mike McLeod, Hugh Jones, Julian Goater, Steve Kenyon, Karl Harrison, Carl Thackery, Kevin Forster, Steve Binns, Tim Hutchings, Gary Staines, Richard Nerurkar, and Eamonn Martin, among others.