 He is a former pupil of Trinity Catholic High School, Woodford Green, he was initially a product of Southend United's youth set-up, although he departed for non-league football and played at Grays Athletic, Wingate & Finchley and Harlow Town.Brentford signed Harrold from Harlow Town in July 2003.He showed early promise in the 2003–04 season when he scored a hat-trick against non-league Gainsborough Trinity in the FA Cup, which made him the youngest-ever Brentford player to score a hat-trick.