By Preeti Upadhyaya, MarketWatch LONDON (MarketWatch) -- U.K. stocks traded lower on Tuesday as the market awaited comments from U.S. Federal Reserve Chairman Ben Bernanke and as security firm G4S PLC got hit with a downgrade following its Olympics-contract debacle. The FTSE 100 fell 0.4% to 5,641.32. Bernanke's testimony in Washington is eagerly anticipated, with investors keen to hear if he will make an announcement about a possible third round of quantitative easing by the U.S. central bank. London investors also digested data on U.K. consumer prices, which fell 0.4% to 2.4% in June from May. "U.K. inflation dropped sharply in June to its lowest since November 2009, further alleviating the squeeze on incomes and helping to revive consumer spending," said Chris Williamson, chief economist for Markit, in a note. "However, the same factors that helped push inflation down may soon reverse and drive inflation higher again in coming months," he added, citing prospects for rising food and oil prices. Among individual movers, shares of G4S extended losses from Monday, falling 5.9% as it was downgraded to neutral from buy by Bank of America Merrill Lynch. The firm recently announced it expected to lose up to $78 million on its Olympics contract after coming up short in terms of security staff. The London Games begin on July 27. Also lower, plumbing firm Wolseley PLC dropped 3.1% following an announcement that it will "explore strategic options" for its businesses in France amid difficult business conditions in Europe. Shares of Rio Tinto PLC (RIO) fell 1.9%. The mining giant reported strong second-quarter earnings, but Chief Executive Tom Albanese cited "global economic conditions and sentiment" as reasons for being cautious moving forward. Further weighing on the index, shares of Vodafone Group PLC (VOD) moved down 0.9%. National Grid PLC shed 2.9% to 662 pence after Societe Generale reduced its target price to 642 pence ($10.03) from 682.5 pence. CSR PLC rocketed 31% following news that Samsung Electronics Co. would acquire the U.K.-based semiconductor firm for $310 million. Energy firms also were on the rise as oil prices advanced, with heavyweight BP PLC (BP) up 0.4% and AMEC PLC gaining 1.2%.