His injuries are horrific: concussion, broken nose and two lost teeth. The assault, which left David Dao bloodied, has been seen by millions. Yet what is really shocking is that Dr Dao, who had paid for his ticket, was attacked by people called in by the airline he was travelling with: he was one of its customers.

Aggrieved travellers from around the world have seized on the brutal treatment of the 69-year-old Vietnamese-American doctor as a symbol of all that is wrong with air travel today, from cramped legroom to carry-on fees.

Dr Dao suffered his injuries at the hands of airport police in Chicago as they forcibly removed him from an overbooked United Continental flight. But by the end of the week, he had emerged as an Everyman figure in a broader corporate morality play about how companies should treat their customers — and what they should say and do when things go badly wrong.