An EasyJet flight from Manchester Airport was delayed on Friday evening after a man "incorrectly" boarded the plane, the airline said.
The passenger, who had been due to fly on another EasyJet service, gained entry to the Milan-bound flight in error.
All passengers were required to disembark as extra security checks were carried out in line with standard procedure.
Greater Manchester Police (GMP) said a man had "embarked on a flight without the correct documentation".
Authorities found nothing suspicious onboard, and there was no indication of any terror-related activity.
An EasyJet spokesman said that the flight was "subject to additional security checks, in line with procedures, due to a passenger incorrectly boarding the flight".
"Safety and security is our highest priority and so we will now work with our ground partner at Manchester Airport to understand how he was able to board the flight."
A GMP spokesman said last night that a man in his 20s was arrested on suspicion of hiding themselves with the purpose of "being carried in an aircraft without consent and intentionally or recklessly causing public nuisance".
An EasyJet spokesman said they were "not able to provide further details while [the investigation] is ongoing".
