(Reuters) - British merchant bank Close Brothers Group Plc on Friday reported a 5.1% percent rise in loan book this year on the back of strong lending in its banking division, but flagged low trading volumes at its market maker unit.The mid-cap firm, which provides loans and wealth management as well as securities trading services, said its loan book stood at 7.6 billion pounds with commercial delivering good growth across the portfolio.Close Brothers said in May that it expected a solid result..