An air passenger sparked a security scare at Gatwick airport after boarding a plane to look for a lost wallet, as the aircraft was being cleaned.
Security has been tightened over the last week
Travel company Thomas Cook is calling on airport operator BAA to investigate how the man managed to get on one of its jets at 0110 BST on Tuesday.
The man, described by the firm as Asian and holding a briefcase, was challenged by cleaning staff, who called security.
Sussex Police said he was questioned and allowed to complete his journey.
The man had been a passenger on a Thomson plane.
A police spokesman said he attempted to retrace his steps after leaving the flight but "got confused" and boarded the Thomas Cook aircraft by mistake.
"This wasn't a breach of security," he added.
"He had not come through security in to the airport yet and went back to look for his wallet.
"When he was stopped, his story checked out and afterwards he reported his lost wallet to lost property.
"He had not entered the terminal building yet."
A statement from Thomas Cook said the man had been "sweating profusely" and was spotted in the cabin close to the plane's cockpit.
"Thomas Cook Airlines has asked BAA Gatwick to explain how a passenger with no Thomas Cook travel documentation was able to access a restricted area," a spokeswoman said.
BAA said the man had arrived on a flight from Ibiza and inadvertently boarded the Thomas Cook aircraft.
It said he made his way on to the plane by smashing an alarmed door lock giving access to the bridge leading to the plane.
Security staff later carried out a full search of the aircraft and nothing was found, it added.
"We don't believe that was a serious breach of security," David Stretch from BAA told the BBC.
"It was a genuine mistake."