Heritage, the Lloyd's insurer, raised £5.4m in a non-underwritten share offer to push its total managed capacity up to £200m for next year.
The group will share the resulting £12m extra capacity between its three syndicates.
Earlier this year, the group launched Syndicate 3245 which focused on professional indemnity.
A company spokesman said 64% would be used on Les Rock's Syndicate 1200 which writes mainly short tail Fortune 500 property risks.
Two thirds of the rest would be used on Syndicate 1245, which writes programme business with a focus on property. The remainder would be used on Syndicate 3245.
The share issue was nearly 90% subscribed, the company said.
The shares were offered on the basis of two new shares at 60p for each existing share held. They were also offered to new shareholders.
Existing shareholders took up half the shares and directors and staff took a further third. New shareholders took about a fifth.
Among the new shareholders was part of the Epic investment group, whose shareholders include Benfield, the world's largest reinsurance broker, and Brit Insurance Holdings, the Lloyd's-based insurance group.