Complex sentence: Trade union members in the United Kingdom have been blacklisted by employers using the services of the Economic League (UK) which operated between 1918 and 1993, and The Consulting Association which took over this role until it was closed down in February 2009.
Split into simpler sentences: Trade union members in the United Kingdom have been blacklisted by employers. They used the services of the Economic League (UK), which operated between 1918 and 1993, and The Consulting Association, which took over this role until it was closed down in February 2009.