In March, Jason played a key role in securing England's Grand Slam with a win over Ireland at Lansdowne Road. In August he captained England for the second time in World Cup warm-up match, crushing Wales 43–9 at the Millennium Stadium in Cardiff. It was Leonard's proven ability to play both loose-head and tight-head and experience which earned him a spot in England's World Cup Squad. During the tournament, he made appearances in all seven matches of the 2003 World Cup, including the semi-final against France where he overtook Phillipe Sella as the world's most-capped player. During the 2003 tournament, Leonard appeared in his second World Cup final as a second-half substitute for tight-head prop Phil Vickery, playing a vital role in reducing England's high penalty count at the scrum. The then coach Clive Woodward later wrote in his autobiography that Leonard's introduction was the key substitution which helped England to win the match.
