Educated at Teddington School, Castledine had a ten-year career as a professional footballer, playing in the Premier League for Wimbledon and in Division 1 for Wycombe Wanderers.
He began his career with Wimbledon as an apprentice in 1989, turning professional for the 1991–92 season and making his debut in the old Football League First Division against Norwich City in a 1–1 draw on 25 April 1992.
He also had a loan spell with Wycombe Wanderers in the 1995–96 season, scoring three goals in seven Division Two games, and finally left the Dons on 7 July 2000.
[1] Immediately after his football career, Castledine become a television presenter, hosting BBC One's Big Strong Boys and Houses Behaving Badly.
He is married to TV presenter Lucy Alexander; the couple have two children, Leo, who is a footballer for Chelsea, having also played for Wimbledon F.C.,[4] and EastEnders actress Kitty.