This is the British branch of Japanese company Koei Co., Ltd.
It was created by Koei in 2003 as a subsidiary for the European market, and followed Koei Canada in 2001 which served a similar purpose for that country. Originally, Koei Tecmo Europe was known as simply Koei Europe, or Koei Ltd. Its name was changed to Tecmo Koei Europe in 2009 when the two developers merged. As of 2014, it's been renamed Koei Tecmo Europe.
As a subsidiary, the company mostly publishes Koei Tecmo games in its region.