British American Tobacco has sold 2.5% stake in ITC Ltd. for Rs 12,100 crore through a block deal.After the stake sale, BAT's holding in ITC slips to 17.81%.The proceeds from the block deal will be used to extend the Group's share buyback program by approximately Rs 2,310.6 crore.ITC shares fell by 4.82% to Rs 413 apiece post the block deal announcement, the lowest since April 9.