 His musical career began at age 16, as an orchestral cellist with the London Symphony Orchestra, playing under such conductors as Sir Henry Wood, Richard Strauss, and Leopold Stokowski.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".