In 1952 Weldon became assistant to Sir John Barbirolli at the Hallé Orchestra and remained in that position until his death. In 1955 and 1956 he also conducted the Sadler's Wells Ballet. He became well known for his love of sports cars. While in Manchester, Weldon took charge of the Hallé summer seasons of promenade concerts, and many industrial concerts around the north of England. He frequently conducted in London and abroad, made broadcasts and many records.