Manchester mayor and the elected police and crime commissioner Tony Lloyd has labelled the drama that saw Manchester United's final Premier League fixture against AFC Bournemouth cancelled a "fiasco".
Lloyd called for a full inquiry into how a dummy bomb could have been left behind by a private security company following a training exercise at Old Trafford.
The device was discovered in one of the stadium's toilets just hours before kick-off on Sunday and prompted a full evacuation and abandonment of the final-day clash.
Greater Manchester Police had initially said they had found an "incredibly lifelike explosive device" before it was later described as a replica device and removed with a controlled explosion.
But Lloyd said the situation was completely unacceptable and needed to be fully investigated.
"A full inquiry is required to urgently find out how this happened, why it happened and who will be held accountable," he said.
"This fiasco caused massive inconvenience to supporters who had come from far and wide to watch the match, wasted the time of huge numbers of police officers and the army's bomb squad, and unnecessarily put people in danger.
"Whilst this in no way demeans the professionalism of the police and stewards responsible for getting the fans out, or the supporters' calmness and cooperation during the evacuation, it is unacceptable that it happened in the first place."
The Premier League fixture has been rescheduled for Tuesday, with United confirming it would refund all tickets purchased for the game and allow free entry.
The gesture is estimated to cost the club £3million.