British engineer Charlie Northfield, 48, was detained by the Gambian government last month.
The firm has since moved out of Gambia and written off all assets in the area. It is now using FD as it campaigns for Northfield's release.
Carnegie MD Alan Hopkins said: 'We were duped into allowing Charlie to return to the country and Gambia has ensured we cannot get him out of jail quickly.
'They seem intent on a swift trial. We call on all governments with relationships with Gambia to take heed of this situation.'