BJK&E won Fujitsu's account from Carat in 1997, and retained the combined business following the merger with Siemens.
Optimedia, which handles Siemens' mobile phone business, does not work with the Fujitsu Siemens operation.
"From time to time it's worth looking at the market to compare our existing agency with its rivals,
Fujitsu Siemens' marketing director, Mel Taylor, said. "In this instance we have concluded that BJK&E continues to provide us with the best all-round offering."