Brit is to transfer all its UK motor, property, employers' liability and public liability business out of Lloyd's into the London company market.
The business will move to the group's FSA-regulated company, Brit Insurance Ltd (BIL), from its Lloyd's Syndicate 2987 as policies are renewed.
The change comes after BIL was last week granted licences to conduct all forms of UK insurance and reinsurance.
Brit group owns 100% of both its Lloyd's operation and BIL, giving the group the freedom to choose where it writes business.
BIL chief executive Dane Douetil said: "Lloyd's isn't the right place to write some lines of business, in our opinion. But we are not saying Lloyd's is bad, the insurance company is good. You need both."
Personal lines business was 3% more expensive to transact at Lloyd's than at an FSA-regulated company. The group plans to write £100m of motor business next year, leading to savings of £3m if it is written in the company market.
The move will allow Brit to expand some of its Lloyd's business.
Douetil said: "We're looking to expand marine, reinsurance and property and casualty at Lloyd's."