What was initially described by police as an "incredibly lifelike explosive device" was left in a toilet cubicle inside United's ground during a training exercise last week and its discovery ahead of kick-off on Sunday caused the stadium to be evacuated.

Chris Reid, the managing director of Security Search Management & Solutions Ltd who had been hired by Deacons Canines to carry out practical training exercises at the stadium last week, said he took full responsibility for the fake explosive being left behind.

Manchester United executive vice-chairman Ed Woodward said yesterday that the item had been signed as returned before the sub-contractors left the stadium and because the device was non-explosive it could not have been detected by sniffer dogs during their routine sweep of the ground.

And speaking outside his home in Biggin Hill, south-east London, an emotional Reid - a retired Scotland Yard police officer - said: "This mistake is entirely mine. I have to take full responsibility for leaving a training item behind on Wednesday.

''I am absolutely devastated that a lapse in my working protocols has resulted in many people being disappointed, frightened and inconvenienced.

"Nothing I can say will rectify that.

''Unfortunately an item that was placed in the male WC was not recovered, as I had a similar item that I had not used.

"I saw this and made the mistake in thinking that the item in the WC had been brought back when found by the attendees, as had other items I had checked into the bag.

''The item had a small white label on it which said: 'Training aid - if found contact SSMS', and my telephone number.''

He said he had been at home when events occurred and watched it on television.

The evacuation of the Stretford End and Sir Alex Ferguson Stand began around 20 minutes before the scheduled kick-off of 3pm after an announcement was made for security personnel to invoke ''operation red code''.

The device was discovered in toilets between the two stands.

Shortly after 3.15pm those remaining in the stadium were informed the game was off.

Army bomb disposal experts called in by officers carried out a controlled explosion on the device in the north-west quadrant of the ground at 4.30pm.

Woodward had praised stadium staff for the way they reacted to the incident.

He said in a statement: "The safety of the fans is our number one aim at every event we host at Old Trafford.

"Overall, I'm proud of how our staff responded."

The game has been arranged for Tuesday evening, four days before Louis van Gaal's United play Crystal Palace at Wembley in the FA Cup Final.

United announced all fans who bought a ticket for Sunday's game will receive a refund and gain free entry to the game, while Bournemouth have put on free coach travel for their supporters.

United need a point to secure fifth place and entry to the Europa League group stage, while a highly-unlikely 19-goal win would lift them above Manchester City into the fourth Champions League spot.