LONDON, Feb 15 (Reuters) - Britain's biggest car dealer, Pendragon Plc , said on Wednesday it had purchased an a further 17.8 percent of Reg Vardy Plc shares for 900 pence per share. Pendragon said it had purchased just over 10 million Reg Vardy shares in the market and had now bought, agreed to acquire or received acceptances for approximately 73 percent of the total issued share capital of Reg Vardy.