His birth was not registered until the following year, and to avoid a fine for late registration his father pretended Harry was born on 2 March 1910, which date has entered many reference works.
At age 18 he moved to become a pupil of Arthur Catterall at the Royal Manchester College of Music, and in 1929 joined the Hallé Orchestra.
In 1936 he left to become the leader of his own eponymous string quartet, with Edward Silverman, Douglas Thompson and William Pleeth.
During the war, Silverman died of a heart condition, Thomson was killed while learning to fly and Pleeth joined the army, so new string players were brought in.
Blech became a conductor in 1942 under wartime conditions, and formed the London Wind Players from the RAF Symphony Orchestra.