The official refused to give a penalty when Neil Lennon was fouled by Rangers full-back Steven Smith in the area.

Celtic were leading at the time through a Thomas Gravesen goal but were held to a 1-1 draw when Brahim Hemdani netted for Rangers with three minutes to go.

Lennon and Hoops boss Gordon Strachan were both fuming about the penalty incident after the game, which could have allowed them to win the match and extend their Scottish Premier League lead over Rangers to 19 points.

After watching the incident again on television, Clark admits he called it wrong.

Speaking on the Whistleblower section of the Scottish Football Association's website, he said: "I got the opportunity to watch the incident for the first time last evening (Monday) and, yes, it should have been a penalty kick.

"In penalty area situations a referee tries to take up the best position possible and, as play developed from the left, I moved with it and thought I was well-placed.