The sale follows Atkins’ disposal of its asset management business to Sodexo on 1 December 2011.
The stake has been bought by a subsidiary of HICL Infrastructure Company Ltd, which is already a partial owner of the project and now has a 56% shareholding.
The sale prices was £15m but £600,000 was deducted for previous loan notes.
The redevelopment of Colchester Garrison, completed in 2008, is one of the largest defence accommodation PFI projects to date and saw the construction by Sir Robert McAlpine of more than 110 buildings across the 185 hectare site.
The garrison is home to the 16th Air Assault Brigade, 3,500 military personnel and 700 civilian staff.
Catering, cleaning and transport services are provided by Sodexo Defence Services Limited. Sodexo Property Solutions Ltd (formerly known as Atkins Facilities Management) is responsible for estate and grounds maintenance, contract management and security, waste management and lifecycle.