The defender left the Iron on a free transfer last summer after three years at the club but was unable to break into the first team at Vicarage Road and was loaned back to Alan Knill's side for the second half of the season. The 27-year-old made 19 appearances for Scunthorpe during that loan stint and played a key role as the club avoided relegation from League One. Scunthorpe had wanted to sign Mirfin on a permanent deal all summer but were initially rebuffed by the Hornets' previous owners. However, following the takeover, Mirfin has now been allowed to leave.