Stock prices ended slightly higher Thursday after a dull day of trading on the London Stock Exchange, as the market failed to take direction from an eagerly awaited string of British economic reports. Instead, trading activity focused on selected issues, especially those involved in takeover situations, dealers said. The Financial Times-Stock Exchange 100-share index was up 3.0 points, or 0.2 percent, at 1,833.9, its best level for the day. The index moved in a narrow range throughout the day, losing at most 4.2 points shortly after the start of dealings. But shares rose late in the day on the back of early gains on Wall Street..