The Manchester Arena suicide bomber was rescued from the civil war in Libya by the Royal Navy three years before he killed 22 people at a pop concert.
Salman Abedi was 19 when he boarded the HMS Enterprise in Tripoli in August 2014 with his younger brother Hashem and more than 100 other British citizens.
It is understood Abedi’s name was on a list of stranded citizens handed to the crew in charge of the evacuation.
The vessel took them to Malta where they caught a flight back to the UK.
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In May last year, he killed 22 people including seven children at an Ariana Grande concert with a homemade suicide vest.
A Government spokesman said: “During the deteriorating security situation in Libya in 2014, Border Force officials were deployed to assist with the evacuation of British nationals and their dependants.”
Abedi was being monitored by security services when he travelled to Libya, but his case was closed a month before his rescue.
The Anderson review into the Manchester attack found that the decision to close Abedi’s case as a “subject of interest” was sound, based on the information available to security services at the time.
A Government source told the Daily Mail: “For this man to commit such an atrocity on UK soil after we rescued him from Libya was an act of utter betrayal.”
Hashem Abedi is held in jail in Libya by a militia group, but the British Government has requested his extradition to face trial for his involvement in the attack.
The request has so far been refused.