Carl admitted that he was Tom King's killer in 2007 but the secret has so far remained within the family.
In a webchat, Blyth said that it will remain under wraps as he does not want to write the character out of the show.
"Always a tricky one and one that I inherited because for Carl to get his comeuppance and justice to be done, would mean Carl leaving the show," he replied.
"As I am a big fan of Tom [Lister] I much prefer to keep that secret in the bottom drawer for now."
