TRANSAMERICA <TA> TO BUY SEDGWICK <SDWK.L> UNIT Transamerica Corp's Transamerica Insurance Co said it signed a definitive pact to buy a 51 pct interest in Sedgwick Group PLC's River Thames Insurance Co. Transamerica will buy 11 mln newly issued Class A shares of River Thames for 2.23 dlrs per share. Sedgwick wil retain a 49 pct interest in River Thames, which is a property liability reinsurer. The agreement, subject to shareholder approval, is expected to close by the end of the year, the company said. In 1986, River Thames reported net premiums written of 36 mln dlrs.