Complex sentence: Offices opposite the original store served as the headquarters for the Great Mills company, but stood largely empty after the Focus acquisition, mainly used as storage for Focus DIY equipment, and also for a small part, as a call centre for the same company.
Split into simpler sentences: Offices opposite the original store served as the headquarters for the Great Mills company, but stood largely empty after the Focus acquisition. The former offices mainly used as storage for Focus DIY equipment, and also for a small part, as a call centre for the same company.