With Liverpool, Liddell competed in the various regional leagues that the FA assigned the club to and scored 82 goals in 152 matches between 1940 and 1946. He debuted on 1 January 1940 against Crewe Alexandra, scoring after two minutes in a 7–3 win. In his formative years, Liddell credited Matt Busby and Berry Nieuwenhuys as significant influences. He volunteered for the Royal Air Force and, despite wanting to qualify as a pilot, was trained as a navigator because of his proficiency at mathematics. After being mobilised in December 1942, Liddell guested with Chelsea and Cambridge Town. He broke his leg in a friendly kickabout while stationed in Bridgnorth, which required admission to the RAF Remedial Centre at Blackpool.