A terror suspect and professional criminal with 17 aliases has been working at Britain's busiest airport.
Despite being on an official terror watchlist, Mohamed Abdullahi Mohamud, 31, who had an 11-year criminal record, was able to access the runway at Heathrow, The Mirror reported.
His crimes included threats to kill, robbery, assault and money laundering.
He was interviewed five times by anti-terrorist officials in the past two years, after two terror charges that were later dropped, because of insuficent evidence.
In 2015, he was ordered to go on the sex offenders register for 10 years, after he was convicted of sexual assault.
He has served a total of five years in prison.
In the alarming security breach, Mohamud was given a security pass and allowed to start working as a kitchen porter in a first-class lounge, without a full background check.
An investigation was launched, after Mohamud contacted The Mirror, claiming to have been offered the job, despite being known to anti-terror officials.
He also claimed no background checks had been carried out and he wanted to expose the security loophole.
Following the investigation, it was found he had lied about his multiple convictions to recruiters, when he applied for his job, which he took up through the SM Global Consultancy Ltd agency on Monday.
For five days, he had airside access in Terminal 3, which serves 17.7 million passengers on 89,000 flights a year.
A security source said a full criminal record check through the Disclosure and Barring Service search could have taken around four weeks, so Mohamud could have gone a month undetected.
His security pass was revoked and his employment terminated.
"Even if he hadn't been a terror suspect, his convictions should have meant he wasn't allowed anywhere near a plane, let alone our busiest airport."
A spokesman for SM Global Consultancy said all security procedures set by Heathrow Airport and the Civil Aviation Agency had been followed.
Mohamud had lied by declaring he had no criminal convictions, but the problem was all his other documentation was genuine, he said.
"He provided us with all the relevant information to begin carrying out our checks, which SM Global Consultancy Ltd do for all workers.
"I am not sure how he has managed to get on the tarmac, but he would be fully screened at every crucial entry point with an escort.
"As a recruitment business, it's our customers' responsibility to supervise and manage the employees supplied."
A spokeswoman for Heathrow Airport told The Mirror: "No security breaches have been made and Heathrow airport remains safe.
"The conditions of this temporary pass required the individual to be constantly escorted by a permanent member of staff.
"He was also subjected to a robust and thorough security search each time he gained access to certain areas.
"Heathrow is compliant with Government regulations."