The head of the firm which left a dummy bomb at Manchester United’s Old Trafford stadium said he took full responsibility for the blunder which led to thousands of people being evacuated from the ground.

Chris Reid, the managing director of Security Search Management & Solutions Ltd, said he took full responsibility for the fake explosive which sparked Sunday’s security alert and forced the postponement of United’s Premier League game against Bournemouth.

The dummy bomb, initially described by police as an “incredibly lifelike explosive device”, was left behind after a training exercise last week.

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.”

Reid said the device had been left on a hook behind a door of a men’s toilet cubicle and “was not concealed in any other way”.

He added: “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.” Security Search Management & Solutions Ltd was hired by Deacons Canines to carry out practical training exercises at the stadium last week.

Reid told reporters on Monday that after the exercise for five dog handlers he had checked a number of fake items into his bag, having previously recorded their position on a ”trapping sheet”.

He said: ”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.

”This item concerned was a mock-up of a pipe bomb, it was approx eight inches long, brass fittings at each end, a length of black flexible lead and a mobile phone taped to the pipe with black tape.

”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 involved 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 in the quadrant 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.

The game was called off after discussions between the Football Association, the Premier League and police and has been rearranged for Tuesday at 8pm, four days before United play Crystal Palace at Wembley in the FA Cup final.

United earlier on Monday said the suspect device could not have been detected by a routine sniffer dog search.

Executive vice-chairman Ed Woodward 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 facts are:

“On the discovery of a suspect package, the police and the club worked quickly and closely to identify the threat, make people safe and evacuate the ground calmly and efficiently;

“Fans of both clubs behaved impeccably and the evacuation – the first of its type in the UK – was a complete success;

“Following investigation, the device proved to have been left in error following the training of dog handlers by a sub-contractor;

“The contractor had signed the device as having been recovered along with the 13 other devices at the end of the exercise;

“That device could not have been detected by sniffer dogs on the routine matchday search of the 100 Club, as it contained no explosives and was used in an exercise training handlers not dogs.”

Woodward promised the matter would be investigated but has praised those involved in what proved a highly efficient evacuation.

He said: “Once a live situation was identified, the club and police had no option but to treat the matter as a potential terror threat; we could not have assumed it was a training exercise error. Presented with the same situation in the future, we would take the same action.

“We have worked very closely with the police and counter terrorism specialists for many years now and enjoy their support on a daily basis.

“We are conducting a detailed evaluation with the help of the police and will share our findings across the rest of the game. Valuable lessons will have been learned from yesterday’s events and it is important that those are shared with other stadium operators to ensure that the safety of the public remains the first duty of us all.”

Woodward’s update came after a strong call from Greater Manchester’s police and crime commissioner for answers.

Tony Lloyd, who is also the mayor of Greater Manchester, said: “I think United have to come up front with all this because in the end it’s their reputation, but it’s also public safety and both those two really do matter.

“Fiasco is the right word. It was shambolic. Of course United are a huge organisation. It wasn’t the fact they’re the world’s richest club – that they are – it was the fact that the security had missed something that in the end ought to have been found.”