A whistleblower involved in training staff for security firm G4S has told Sky News he believes there is a 50-50 chance someone could carry a bomb into one of the Olympic venues.
He alleges that because of the pressure to recruit staff corners have been cut and some of the staff are not up to the job.
The employee, whose identity Sky News is not revealing, said there is a "no fail" policy for security staff and all recruits passed the course regardless of how competent they were.
Staff - who had received two days of intensive training operating X-ray machines to detect lethal weapons and explosives - failed to spot decommissioned hand-grenades and firearms during a test.
Security officers asked to pat down a volunteer with a deactivated 9mm pistol in his sock failed to find the weapon.
Another guard picked up a fake improvised explosive device put through an X-ray scanner as a test and waved it around, despite being trained never to touch suspect bombs.
A trainee, who failed to keep track of which personal items belonged to whom, enabled a volunteer to put a mock bomb through the X-ray machine then disappear into the crowd.
All these members of staff were later passed as having successfully completed training. They were told to collect their security badge and uniform and were cleared to work in the Olympic park.
The whistleblower who contacted Sky News has extensive military and professional security training and is an expert in weapons and IED detection.
He said: “I can see so many security loopholes for this event. Security staff are given a very short time to achieve their training and there is a very slack approach.
“During my employment I planted pretend IEDs, decommissioned weapons, knives and other large metallic objects on students and sent them through the metal detectors.
“They’re not being seen by X-ray staff and they’re not being picked up during physical searches, so the training is completely insufficient.
“The people making these mistakes are then given a tick in the box at the end of the day, sent round the corner to collect their uniform and sent home to await an email with their start date.
“Ninety-nine per cent of personnel coming through have no security background; many have language problems so they won’t be able to communicate with ticketholders and many completely lack confidence.
“We found out we’d won the bid for the Olympics in plenty of time. If they had recruited and vetted personnel from day one I don’t think there would be a problem.
G4S said it was committed to ensuring the games were “safe and secure”.
In a statement, the company said: “This is an unprecedented and very complex security recruitment and deployment exercise which is being carried out to a very tight schedule.
“We have made very significant progress - we already have around 4,000 people at work across 100 venues.
"We currently have over 9,000 additional people going through the final stages of the required extensive training, vetting and accreditation process.
“We have encountered some delays in progressing applicants through the final stages but we are working extremely hard to process these as swiftly as possible.
“We understand the Government's decision to bring in additional resources and will work with LOCOG, the military and other agencies to deliver a safe and secure Games."