SHARES on the London Stock Exchange closed lower as investor concerns grew about the prospects of an interest rate increase next month. The blue-chip Financial Times Stock Exchange 100-share index closed at 3,300.8, down 9.9 points from the previous close. A half an hour before the close volume of shares traded was 454.6 million, up from 409 million the same time on Monday. Analysts said the market had run out of momentum after posting strong gains last week as well as being undermined by growing anticipation of an interest rate increase in June. Input prices data for the year to April, released on Monday, showed a rise of 11.5 per cent, well above market forecasts and fanning fears of a tightening of monetary policy as early as next month. Analysts said weakness on Wall Street was also weighing on London equities. Gases group BOC rose 12 pence to GBP7.85 as broker upgradings followed the release of positive interim results. Television broadcaster Carlton Communications gained four pence.