Henderson Global Investors Ltd., the manager of $108 billion in assets, plans to build an office complex capped by a 34-story tower in the City of London financial district as developers tap the area’s growing insurance market.

The project at 40 Leadenhall Street sits within a cluster of skyscrapers in the City’s insurance district and will accommodate 7,000 workers, Henderson said today in an e-mailed statement. The development will have 910,000 square feet (84,500 square meters) of offices and shops and will cost 391 million pounds ($623 million) to build.

Developers such as British Land Co. and Land Securities Group Plc are building towers close to the Lloyd’s of London insurance market as the industry expands. Insurers accounted for 20 percent of all office space that companies agreed to lease in the 12 months through March, compared with about a 5 percent average in the two years through 2007, according to data compiled by Jones Lang LaSalle Inc.

Henderson’s project will be be completed by 2019 “at the earliest,” Nick Deacon, director of property at Henderson, said by phone. The company plans to secure tenants for 300,000 to 350,000 square feet of space before beginning construction, he said.

British Land’s tower at 122 Leadenhall Street nicknamed the Cheesegrater secured tenants including Aon Plc and Amlin Plc. Land Securities’ tower at 20 Fenchurch Street called the Walkie Talkie, reached lease agreements with Markel Corp., Kiln Group and Ascot Underwriting Inc.