KIRSTIN RIDLEY  BRITAIN's Serious Fraud Office (SFO) has closed its four-year bribery and corruption investigation into the UK subsidiaries of KBR Inc, a U.S.-listed engineering, procurement and construction company. The investigator and prosecutor said yesterday that it had not uncovered sufficient evidence to pursue the case. KBR said it was "pleased and supportive" of the decision, which followed similar announcements by the U.S. Department of Justice and Securities and Exchange Commission that put "a final conclusion to this matter". The closure of the case is the latest in a string of major investigations shut under SFO head Lisa Osofsky. Inquiries…