Nick Rnjak, the lead power underwriter with AEGIS Energy Syndicate 1225, is leaving the company.
In a statement the company said that Mr Rnjak, who has been with AEGIS since late 2004, "has played a significant role in the syndicate's development."
AEGIS will announce Mr Rnjak's successor in the near future.
In a related development, the announcement of the business's new Active Underwriter is also expected soon.
AEGIS London provides cover for a wide range of clients in the global energy market, and has expanded its' team to 70 in last five years.
The AEGIS Energy Syndicate 1225 currently has a capacity of £221 million.