Complex sentence: His first professional scriptwriting credit came when he wrote the radio drama "The Long Stairs", broadcast by the BBC on March 1 1950 and based on a historical mining disaster on the Isle of Man.
Split into simpler sentences: His first professional scriptwriting credit came when he wrote the radio drama "The Long Stairs", broadcast by the BBC on March 1 1950. This was based on a historical mining disaster that had occurred on the Isle of Man.