St. Paul International Insurance has conditionally agreed to acquire the renewal rights for the £20 million a year commercial business of Zenith Commercial.
Martin Hudson, general manager at St. Paul International said: "This deal will provide a strong base of new business growth in several of our established industry sectors as well as in the commercial middle market.
"It will also enable us to accelerate our plans for the launch of a new product targeting selected middle-market commercial risks."
Zenith Commercial managing director David Drew said: "We are delighted to be joining The St. Paul where we will benefit from both long term security and increased capacity to enable our skilled underwriting and risk management team to support the successful development of a new mid-market account."