A British Airways passenger was restrained after entering the business class cabin of an aircraft.
Kwame Bantu, 65, of south London, said his hands and feet were tied up by the crew on the flight from London Gatwick to Jamaica.
He said he moved from economy to business class because he was feeling dizzy and needed more room to stretch his swollen leg.
The Boeing 777 aircraft was diverted to a Portuguese air force base on Terceira, an island in the mid-Atlantic where Mr Bantu and fellow passenger Joy Stoney – who says she tried to help him – were removed from the plane.
He asid: “They ambushed me. They tied my feet, my shoulders and my arms and they left me in my seat.
“I was completely humiliated, my human rights had been taken away from me.”
Ms Stoney, a 40-year-old businesswoman from Yorkshire, added: “The way they restrained him was absolutely preposterous.
“They restrained him by his shoulders via his neck and hands with straps. His ankles were strapped and on top of everything, they handcuffed him.”
A BA spokesman insisted that caring for customers “is our highest priority”.
He said: “We take great care to handle these difficult situations as sensitively as possible. Our cabin crew and one of our pilots repeatedly asked a customer to return to his booked seat in economy after he sat in our business class cabin without permission.
“He repeatedly refused, verbally abused crew members and disturbed other customers.
“As a last resort, our cabin crew felt they had no option but to restrain the customer in the interests of the safety of everyone on board and helped him walk back to his original seat.
“Caring for our customers is our highest priority and we are investigating the circumstances surrounding this incident.
” The flight returned to Gatwick and customers were taken to hotels.”
The aircraft initially departed Gatwick for Kingston at 12.35pm on Wednesday.
A Portuguese air force spokesman told news agency Agence France-Presse that the pair will “remain in Terceira and will be questioned by police”.
He added that they had filmed the incident on a mobile phone.
It comes less than three weeks after a video showing passenger David Dao being dragged off a United Express flight in the US sparked widespread outrage.
Dr Dao, a 69-year-old from Kentucky, was seen with a bloodied face after being forcibly taken off the plane by Chicago airport officers who had been summoned by United employees when he would not give up his seat.