Brit Insurance Holdings has bought the commercial book of Creechurch.
Brit will be able to offer renewals to property and commercial combined clients of Creechurch by the end of 2003.
Brit expects the deal to bring in £40m of gross written premium for 2004.
Creechurch chief executive Bruce Graham said: "We have been very successful in building the UK commercial business through our subsidiary, Charrington Insurance.
"The capacity provided by Brit for the property and commercial combined business will enable Charrington to continue to develop this portfolio for the remainder of 2003, allowing Brit to maintain this expansion in 2004."