Complex sentence: He was formerly chief executive of the major British jewellery company Ratners Group (now the Signet Group), and achieved notoriety after making a speech in which he jokingly denigrated the company's products, which caused the company's near collapse.
Split into simpler sentences: He was formerly chief executive of the major British jewellery company Ratners Group (now the Signet Group). He achieved notoriety after making a speech in which he jokingly denigrated the company's products, which caused the company's near collapse.