Threadneedle, the fund manager owned by American Express, has boosted its stake in Attica Asset Management to make it the majority shareholder in the multi-manager business.

Details of the transaction have not been disclosed but Threadneedle said it has increased a 30% stake it bought last year and confirmed it is now the majority shareholder in Attica. Attica was co-founded three years ago by ex-Mercer consultants Derrick Dunne and Guy Davies. Multi-manager firms combine the services of multiple fund managers to create unique investment portfolios in various asset classes and regions.