Clarke was called up for England's 1970 World Cup squad in Mexico, despite being uncapped. He made his debut for his country against Czechoslovakia in the heat and pressure of a World Cup first round match. Clarke scored the only goal of the match from the penalty spot. He remains the last England player to make his international debut in a World Cup finals match. Over the next five years he appeared a total of 19 times for England, scoring 10 goals. England reached the quarter-finals of the European Football Championships in 1972 but did not get through their qualifying group for the 1976 tournament, or for the 1974 World Cup.