Cardiff Local Guide A guide to all Things Cardiff
Second row Down has made a total of 63 appearances for Blues after making his debut against Border Reivers in 2007.
The 26-year-old has now been released to pursue an opportunity at the newly promoted English top-flight club.
Richard Holland, Chief Executive at Blues, said: “We have agreed to let James leave the Blues to pursue other options that he feels will provide him with more regular playing opportunities.
“James leaves the region with our very best wishes and thanks for his efforts during his time with the Blues.”
