In the 1930s Leslie was a member of the Young Communist League, who met in the Challenge Club in Cheetham. His inspiration for joining the league was a strong desire to fight fascism. On 19th July 1936, when Leslie was 19, he was arrested for his anti-fascists activities along with seven other men. Leslie had attended a rally where Oswald Mosley (the leader of the British Union of Fascists) was speaking at an open-air event held at Albert Croft, Collyhurst. The rally was attended by about 5000 to 8000 people, of which around 600 were fascists. Five days later, Leslie appeared before Manchester City Magistrates. He was fined 40 shillings for ‘inciting others to commit an offense under the Public Meetings Act’, ‘acting at a lawful meeting in a manner for the purpose of preventing the transaction of the business for which the meeting was called’ and ‘disorderly behaviour’.