 In the 1950s and 1960s, Leonard, a close friend of cartoonist Gerard Hoffnung's, participated both as conductor and composer, in the celebrated Hoffnung concerts.In 1959, at Leonard Bernstein's request, Leonard conducted the London premiere of "West Side Story".Leonard was Associate Conductor of the BBC Northern Orchestra and Assistant Conductor to Sir John Barbirolli at the Hallé Orchestra (1963-1968).