Before the plane took off from London Gatwick airport the crew noticed that a toilet was displaying the ‘in use' symbol, even though all seats on the plane were occupied, reported 20 Minutes on Wednesday.
The intruder was taken out of the toilet and arrested.
Speaking to the paper, one passenger said everyone was left shocked. “We didn't understand how this man had been allowed to pass through security.”
The plane was subsequently searched, but some passengers chose to disembark, said the witness.
Gatwick airport told the paper that the stowaway, a 25-year-old Swiss man, had a valid boarding pass when he passed through security. However he managed to miss his booked flight to Geneva and tried to get on the next one by stealth.
EasyJet confirmed to the paper that a passenger “boarded by mistake” and said it had opened an investigation to determine how that could happen.
The incident comes just two weeks after a seven-year-old girl managed to get through security and board an EasyJet flight in Geneva without ever showing a boarding card or identity documents.