Born June 1981 in Weston-super-Mare, Somerset, Trego made his first-class debut for Somerset in April 2000 against Oxford Universities. He took two wickets in the match, but was not required to bat. His first appearance in county cricket came two months later, playing a Norwich Union National League game against Sussex. One of the highlights of Trego's debut season came in the Scarborough Festival County Championship match against Yorkshire, where he made an unbeaten 27 batting in Somerset's first innings, followed by bowling figures of 4/84 in Yorkshire's first innings.