Some 129 security guards are having their licences revoked following a BBC investigation into fraudulent colleges.
Tough exams must be passed to be able to work in the security industry. It is a criminal offence to break the rules.
But undercover researchers caught Ashley Commerce College in Ilford sitting exams for students on a grand scale.
The Security Industry Authority (SIA) has begun revoking licences thought to have been obtained illegally.
The licences are in Door Supervision and Public Space Surveillance (CCTV).
'Significant fraudulent activity'
Those suspected of fraudulently obtaining their licences at the school have been contacted by letter and informed of the proceedings.
It comes after the exam board that awarded the allegedly-fraudulent certifications, Industry Qualifications, carried out a four-week investigation into the malpractice at Ashley Commerce College highlighted by the BBC.
In a statement, the exam board said it had found "significant levels of fraudulent activity".
This involved "candidates that had not undergone training, and or had not sat examinations, being included with candidates that had undertaken programmes in the proper manner".
In total Industry Qualifications has now revoked the certification of 251 candidates believed to have obtained it fraudulently, and informed the SIA.
The SIA has warned that more revocations may follow.
Industry Qualifications has submitted the names and addresses of all 251 candidates to the police and said it will pursue action in the civil courts against all of those involved on completion of the police investigation.
Security consultant Will Geddes, managing director of International Corporate Protection said: "What is astounding is that you have 129 falsified licences from one organisation.
"It makes you wonder how many others there are out there.
"The implications of this investigation are far-reaching - there are people out there presenting themselves to the industry with supposedly legitimate licences which are not what they seem.
"It raises big questions about whether people can trust the security guard who walks through their door."
Ashley Commerce College was one of two schools exposed by BBC London.
It offered to "fast track" our researcher to become a door supervisor or even a qualified bodyguard, which the SIA says should take 140 hours of training.
Students had the answers read to them or were given completed exam papers to copy.
Exam dates were falsified and the BBC's researcher was told to write that he was "intermediate at martial arts", despite it being made clear he had had no such training.
To illustrate the gravity of the situation, an SIA licence obtained by the researcher was used to get a job offer to guard a major power station - a vital part of the UK's national infrastructure.