The UK's retailers suffered an unexpected drop in sales during October but remain optimistic about prospects for November, the country's leading business lobby group said today. In its monthly distributive trades survey, the Confederation of British Industry said 38 pct of retailers said their sales in October were up on a year ago, while 42 pct say they were lower. The ensuing balance of -4 pct is the weakest since March's -16 pct. The slide into negative territory was also the first since March.