St. Paul International is buying London & Edinburgh's IFA professional indemnity business from Norwich Union.
Norwich Union acquired the £9m portfolio from London & Edinburgh Insurance in October 1998.
St. Paul has purchased the right to invite renewal of policies as they fall due and will take over the handling of run-off claims.
St. Paul chief executive officer Kent Urness says: "We have been active in PI business in the UK for selected customer groups since 1994. The purchase of this portfolio will establish our position as a market leader for this particular group."