The dramatic evacuation of Old Trafford today was sparked by a fake bomb left behind after a security drill days before, it can be revealed tonight.

Red-faced Manchester United bosses had to admit tonight that the ‘incredibly lifelike explosive device’ which was destroyed by army bomb disposal experts was left there by mistake following a midweek training exercise at the Theatre of Dreams .

Some 50,000 supporters were evacuated from the ground when the alarm was raised about 15 minutes before the kick-off.

United players were warming up on the pitch when they were told to leave.

The club and the police have now revealed the device had been accidentally left behind by a private company following a security training drill.

Assistant Chief Constable John O’Hare from Greater Manchester Police said: “Following today’s controlled explosion, we have since found out that the item was a training device which had accidentally been left by a private company following a training exercise involving explosive search dogs.

“Whilst this item did not turn out to be a viable explosive, on appearance this device was as real as could be, and the decision to evacuate the stadium was the right thing to do, until we could be sure that people were not at risk.”

United executive vice-chairman Ed Woodward promised an urgent investigation.

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He said: “The safety of fans is always our highest priority.

“I’d like to thank the support from the police which was first class and the impeccable response from fans of both teams.

“The Club takes security very seriously and staff are regularly trained with the police and emergency services to identify and deal with these incidents.

“We will investigate the incident to inform future actions and decisions.”

A ‘code red’ was called around the ground through the PA system and fans were told they must leave their seats.

Supporters were evacuated from the Stretford End and North Stands of the stadium initially, before other sections of the ground - which has a capacity of 76,000 – were also cleared.

Watch - Moment match abandoned inside Old Trafford

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Unconfirmed reports suggest the device was found in the executive toilets under the Stretford End.

Once the ground was cleared, army bomb disposal experts were scrambled to the north west quadrant of the stadium, where

they located a phone attached to a pipe.

They then carried out a controlled explosion as fans were ushered away from the stadium.

After examining the remains, Greater Manchester Police tweeted that it was an ‘incredibly lifelike explosive device’, although they added it ‘wasn’t viable’ as a bomb.

A detailed search of the rest of the ground did not uncover any other devices.

The players of both clubs were among the last people to leave the ground as the game was postponed and will now be replayed tomorrow night with an 8pm kick-off, with United also playing in the FA Cup final on Saturday.

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Some fans were pictures climbing over barriers outside the ground during the evacuation, while one Bournemouth fan who had been waiting to get into the ground when it was evacuated described a ‘calm panic’ as people tried to get to the bridge near Hotel Football. However, police bosses praised how quickly both sets of supporters

evacuated the ground, while fans and players thanked the police for taking prompt action.

Police and Crime Commissioner Tony Lloyd said: “Great job keeping public safe @gmpolice @CCIanHopkins @ManUtd @afcbournemouth well done to officers, army and fans, all safe that’s a result.”

He added later in a statement: “It is outrageous this situation arose and a full inquiry is required to urgently find out how this happened, why it happened and who will be held accountable.

“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, as evacuating tens of thousands of people from a football stadium is not without risk.​

“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 last night released a statement which read: “We can confirm that today’s abandoned fixture between

Manchester United and AFC Bournemouth will be played on Tuesday at 8pm.

“We would like to thank

Manchester United’s staff, the police and other emergency services for all their efforts today as well as rearranging the match for this coming Tuesday.

Watch: Stuart Mathieson on a very 'unusual' day at Old Trafford