In 1968, aged 22, Lavender was cast as Private Pike, the youngest member and “stupid boy” of the platoon in the BBC sitcom "Dad's Army". This made him a household name and gave him the great advantage of working alongside a number of experienced actors during his formative years, helping him to hone his acting skills. He appeared in the entire run of the series, and in the spinoff film released in 1971. He appeared in 1974 in one episode of "Man About the House" (While The Cat's Away) as Mark. in the BBC Radio sitcom "It Sticks Out Half a Mile". The sitcom was a radio sequel to "Dad's Army", but ran for only one series. Lavender has continued to be associated with "Dad's Army", and still takes part in occasional fan conventions and cast reunions. He made a variety of appearances during 2008 in connection with the 40th anniversary of the series. These included a reunion with surviving cast members in July, 2008, and an appearance on BBC1's "Jonathan Ross Salutes Dad's Army" in August.