Complex sentence: In the 1920s the street became known as "Britain's Tin Pan Alley" because of the large number of music shops, a title it holds to this day, the Tin Pan Alley Festival is held there each July.
Split into simpler sentences: In the 1920s the street became known as "Britain's Tin Pan Alley" because of the large number of music shops, a title it holds to this day. The Tin Pan Alley Festival is held there each July.