Complex sentence: He was previously Chief Executive of Great Western Ambulance Service between April 2009 and January 2011 and left that service as Unison balloted its members for strike action following changes to terms and conditions for staff-most notably pay and rota arrangements.
Split into simpler sentences: He was previously Chief Executive of Great Western Ambulance Service between April 2009 and January 2011 and left that service. During his time at Great Western Ambulance Service, Unison balloted its members for strike action following changes to terms and conditions for staff-particularly pay and rota arrangements.