PI Direct (PID) completed the acquisition of professional indemnity (PI) underwriting agency Saturn from MMA last week.
Under the terms of the deal, a new holding company was created, which is jointly owned by PID and Saturn management, with investors Penta Capital also holding a stake.
Saturn will continue to trade under its current name, with all of its 25 Buckinghamshire-based employees remaining with the company.
The sale of Saturn represents a U-turn on the part of the agency's management. At the end of last year, Saturn director Michael Cant insisted there was "no intention" to sell the company.
The new company has a combined gross written premium (GWP) of £55m, with Saturn generating around £20m of that total.
PID chief executive Michael Wood said the deal would enable Saturn to benefit from "our solicitors and IFA capacity".
The new company will service around 15,000 PI policyholders, an estimated 10%-15% of market share by number.
Hiscox will now supply all the capacity for Saturn's book - the insurer formerly provided around 60% of the total.
MMA was formerly the major capacity provider for Saturn, with the underwriting agency generating around £16.5m in GWP for MMA.
An MMA spokesman said: "MMA's strategy in the UK has been re-focused in recent months to concentrate on distributing personal and commercial lines in our chosen markets through a widening intermediary network.
"Saturn, as a specialist PI provider, does not fit this business model and so we have been happy to engage in a sale process which provides a satisfactory outcome to all parties."
The spokesman added that the sales process continued to support the intermediary market.
"The vast majority of [solicitors'] risks are being offered early renewal terms,"