LONDON (May 12): THE Manchester Guardian said to-day that it is necessary for British prestige that it keep Hongkong. The editorial continued: 'The best hope lies in both the Communists and the British agreeing to do nothing by which the face of either side is compromised. 'We and the Chinese Communists must agree that it will benefit each side to leave the other alone. 'Communist China has much to lose buy refusing trade and a normal political relationship with the West. It must be shown that Hongkong is internationally useful and that, if incorporated into China, it would quickly lose its importance.'