Complex sentence: The increase in unemployment was substantially due to government economic policy which resulted in the closure of outdated factories and coalpits which were no longer economically viable; this process continued for most of the 1980s, with newer industries and the service sector enjoying significant growth.
Split into simpler sentences: The increase in unemployment was largely due to the government's economic policy, which resulted in the closure of outdated factories and coal pits which had not been economically viable for many years. This process continued for most of the 1980s, with newer industries and the service sector enjoying significant growth.